I can give it a shot. It would be the same for all BB's with 4.1 right?
How To Install Themes on 4.1 OS
Point you Blackberry browser to http://mobile.blackberry.com Theme click the link for 'Themes for 4.1 and higher devices' Click the 'I accept" after reading th T&C. Now you should see a page that has all the themes that are available for your device.
Downloading themes created with Plazmic. If you want to create your own themes please check this THREAD out to see what you need to get started. First you will need the Plazmic theme reader. It can be downloaded HERE along with other themes from Millena Studios. Next install your theme via DM or OTA. Once the theme has be installed sucessfully, reboot your device. Now to to 'Options' then 'Themes' on your handheld. You should see an option to activate the theme. Click on that and you should be all set.