Search for Blackberry themes for your model phone. I’m betting your phone probably has the same software issue mine has, so you would have to download the theme “over the air”. Just go to google and type something like OTA Blackberry themes. Find the one that you like and then type the web address of the theme into the browser on your BB. A prompt should pop up asking if you want to open or save the file, click save.
Here is a Link to a thread about the problem I had (of course I didn’t see this until after I found a way around the problem)
Pinstack has a lot of info about BlackBerry’s including lots of themes.