From a PC at ShopCrackBerry.com:

 

Login to your store account under the App Store tab

 

You will see a list of all your purchased apps as well as their version numbers.  If any application has an update available, click the Download link

 

Choose to download by either SMS or Email. Enter your information and click Send.

 

You will see a confirmation message if successful

 

You will receive and email with the mobile download link

 

Click through the link and Download to install the application/theme update