I know many of us like to browse on the computer for the themes and then send them to the bb rather than browsing from the bb to get the themes, so I thought I'd simplify the How-To process on how to get my OTA links.
I'm a shortcut girl but I realized not everyone knows how to do this and quite honestly I'm too lazy to email these directions to everyone who asks. Sowweeee.. Remember, you don't download to your computer, you still have to download from your BB, but this helps you get more than one link at a time without having to use your BB browser.
1. Find the OTA link posted for the theme that you want for your device. Right click on the link and select "copy link location".
2. Open a new tab or window and compose a new email.
3. Right click and paste the link (or ctrl + v, remember, I luv shortcuts!)
4. If you have more than one theme you wanna download, just repeat and repeat!
(I'd add a description so you know which theme is which, and really you can just save your email in a folder or copy to a new memo. That way you can delete themes to free up space and easily download ones you like again later)
5. Send the email and download away!
After you've downloaded the theme or to change themes:
From your main menu, scroll through to find Options then Themes.
Scroll through until you see the preview you wish to use. 
If you dont see the theme here, you either have selected wrong OS or you have a different device.
Courtesy of Crackberry! Here is the link below as well as what they suggested. How to Free Up Memory on your BlackBerry Smartphone First off, you want to be sure you have a memory card for your device. One of the most important accessories you can buy – a memory card is priceless. It gives you loads of room to store all those ringtones, videos and MP3s that would otherwise eat up your device memory. If you don’t have a memory card, check out the wide selection in the ShopCrackberry.com store. The overall and most obvious way to free up memory is to delete any applications on your device that you do not use. To do this, from your BlackBerry home screen press the Menu key, then go to Options > Advanced Options > Applications The next few things we can do to start freeing up memory are fairly simple as well: Enable Content Compression: Go to Options > Security and enabled Content Compression, this will free up some space. Set Keep Appointments to 15 Days: This won’t make a major difference but will definitely free up some space. Delete the “Help” Application: Once you get the hang of your BlackBerry you don’t really need this app. Go to Options --> Applications, select Help and delete it. Delete the Sample Video: Go to Options > Advanced Options > Applications. Highlight BlackBerry Sample Video, press Menu and Delete. Delete the Unused Languages: You will have an option to remove them from the Application Loader screen. Delete BrickBreaker: Why you ask? Well if you never seem to play it then it just takes up space – so lose it. Delete Pictures: Delete any unwanted images or move them to your memory card. Clean Up Browser Cookies and Cache: Start the mobile browser. Press the Menu key and select Options > Cache Operations. Clear History & Clear Cookies. Reduce Allocated Media Memory: Start the Media App. Press the Menu key. Change the Device Memory Limit to 12mb. Change Save Time for Messages: Click the Messages icon. Press the Menu key and select Options. Select General Options. Scroll to Keep Messages and lower the value. Change Call Log Options: Click the Phone icon. Press the Menu key. Select Options > Call Logging. Change to None (or Missed Calls if you prefer). Remove Unused Apps: You can also remove any unused apps such as Tasks, Memo, BlackBerry Messenger etc. to free up space. All of the standard apps can be removed from the Application Loader in the Desktop Manger. Deleting Old Messages: Deleting SMS messages and emails will save space and reduce lag as well. I tend to delete all my previous SMS messages every morning. Limit Your Themes: Everyone wants to have a good choice of themes, but having only 1 or 2 at a time on your device will save lots of space. Removing Default Items and Modules Now we can get a bit more technical and remove some of the other features that will save even more space. To start, you will need to have your current OS installed on your PC. If you don’t have it you can usually download it here: BlackBerry - BlackBerry Desktop and Device Software Download Sites and install it to your PC. After it is installed, plug in your BB and open Desktop Manager. Do a complete backup of your device (from the Backup/Restore menu). When the backup is complete, close the Desktop Manager and unplug your BB. Delete the vendor.xml file from your PC (should be located in c:\program files\common files\research in motion\apploader). This file is really unnecessary as it only tells your device specifics about your carrier and OS, so we can just trash it. There are certain items that can be removed to save space such as Voice Activated Dialing (VAD), Push to Talk (PTT) on some AT&T Devices, themes etc. Decide what you don’t use and we can remove them from the device. Navigate to C:\Program Files\Common Files\Research In Motion\Shared\Loader Files\xxx\Java on your PC (where xxx is the installed OS version). From here we can do the following: Remove Wallpaper: These two files will most likely have your device model in them but it is essentially what the file name will appear as. (The best way to handle them is to move them to a separate directory - Create a new directory labeled "Removed”) Select the COD file and move it to the “Removed” folder. This will remove all of the pre-installed wall paper, leaving you with a blank background. Remove Default Themes: Themes are supplied by BlackBerry and the carrier. Each device is carrier branded during manufacture; the branding controls the loading of specific theme components. In this case, T-Mobile themes are identified by "100". Other carriers have similar numbers assigned. You can ignore themes with non matching numbers; they will be skipped in the process. Both of the above are needed for normal device operation. You can safely remove the following: Removing these is optional, it will save about 700 Kb. Remove Push To Talk: If you are not using it (your device may not even have it), remove these files: Remove Voice Activated Dialing: Remove Password Keeper: Move all files prefaced with net_rim_bb_passwordkeeper_resource_ to the Removed folder. Connect your device to your PC and run the Application Loader to complete the changes. If there are other applications you want to remove, verify which modules are used with by going to Options > Advanced Options. Choose an application, press the Menu key and select View Properties. All modules are that make up the application are listed.* *Keep in mind, other applications may share modules. Be prepared to restore some of them if you run into problems (that’s why we did a backup first). After these procedures you may also find that Desktop Manager will not recognize your device. If this happens, go to Control Panel > System > Device Manager on your PC and delete you Blackberry Device. Then reconnect it and it should be accepted by the Desktop Manager. If you somehow manage to screw up and brick your device – fear not and read this: How do I Recover a Dead BlackBerry? For more information and help on this topic, visit the How To Increase your BlackBerry's File Free Memory Thread in the CrackBerry Forums.
http://crackberry.com/blackberry-101-how-free-memory-your-blackberry-smartphone
net_rim_bb_media_320x240_b.COD
or
net_rim_bb_media_240 x 260_b.COD 
net_rim_theme_100_320x240_b.COD
net_rim_theme_bbdimension_zen_320x240_b.COD
net_rim_theme_bbdimentions_icon_320x240_b
net_rim_theme_bbdimentions_l_320x240_b
net_rim_theme_bbdimentions_today_320x240_b 
KnJCDE
net_rim_bb_phone_ptt_app
Move all files prefaced with net_rim_vad_ to the Removed folder. 
There's 2 ways to find out your OS for your device.
Method 1 : Find the Options icons: Go to Options > About. It will say Blackberry XXXX (insert device name here) and then v.. blah blah blah. Mine says v4.5.0.110, which equate to OS 4.5. Hooray, we have our OS.
Method 2: From the Home screen: Hold down the left side ALT key and the SHIFT key right below it (arrow aA) at the same time, and hold down the H key. The OS will show across from the APP Version.
TO DELETE THEMES >> Go to Options/Advanced Options/Applications and scroll until you see the theme you want to delete under com_plazmic_theme_blah blah blah theme. Hit the menu button and select delete. It will prompt you to restart to save the changes.
I recommend doing this fairly often to prevent your device from getting laggy. I usually keep about 4-5 themes on my device but I know some people who can keep 8-10.
Zip Files are what you need to install themes via Desktop Manager if you don't have a data plan.
I dont provide zip files on my site but will send them via email for $5 donation.
Step 1. Make sure you have a Blackberry. Seems simple but I'm trying to cover all bases!
Step 2. Know your Operating System (from here on out we will call it OS).To find out your OS, on your BB go to Options/About. It will say Blackberry XXXX (insert device name here) and then v.. blah blah blah. Mine says v4.5.0.110, which is 4.5. Hooray, we have our OS.
Step 3. If you do not have a data plan and need a zip file for desktop manager, I will only provide them with donation and I expect these not to show up on a site without my permission. Please donate and specify in the seller instructions the OS and theme style *bottom dock or today plus*.
Step 4. Download the .ALX and .COD files to your computer from the email or from the theme designer's website if you have another zip file. Connect your BB via USB cable.
Step 5. Launch Desktop Manager on your PC. Usually takes some time to get it loaded (this is why I hate using zip files!) Using the application loader on DM, browse to locate the .ALX and .COD files and select next. Once it has loaded it will reboot your device.
Step 6. To select the theme you just downloaded, go to Options/Themes and scroll to the preview you wish to use. If you dont see the theme here, you either have selected wrong OS or you have a different device.Usually I keep about 4-5 themes on my device before it starts getting laggy. If you have more memory you may be able to manage more than that.
Step 1. Make sure you have a Blackberry. Seems simple but I'm trying to cover all bases!
Step 2. Know your Operating System (from here on out we will call it OS).
To find out your OS, on your BB go to Options/About. It will say Blackberry XXXX (insert device name here) and then v.. blah blah blah. Mine says v4.5.0.110, which is 4.5. Hooray, we have our OS.
Step 3. You need to download from your BB. OTA links are Over-The-Air downloads, so please dont try to open the file from your PC and then email me asking why it doesnt work. :) This is the one question I get asked the most so I am gonna make it bold!
If you do not have a data plan and need a zip file for desktop manager, I will only provide them with donation and I expect these not to show up on a site without my permission.
If you'd like theme changes please donate and specify in the seller instructions what you'd like me to change.
Step 4. If there's only one style (4.5 Bottom Dock OTA for example), the link is in the title, if there are multiple titles then just look for the hyperlinks that say OTA. You need to click on the link from your blackberry. I would suggest bookmarking my site, or copying the address in the header and emailing that to yourself. Select bottom dock or today plus style, and voila. You're done. Yaaay!!
Step 5. To select the theme you just downloaded, go to Options/Themes and scroll to the preview you wish to use. If you dont see the theme here, you either have selected wrong OS or you have a different device.
Usually I keep about 4-5 themes on my device before it starts getting laggy. If you have more memory you may be able to manage more than that.
TO DELETE THEMES >> Go to Options/Advanced Options/Applications and scroll until you see the theme you want to delete under com_plazmic_theme_blah blah blah theme. Hit the menu button and select delete. It will prompt you to restart to save the changes.