its very simple put the theme on your memory stick if you have off the internet 1.Move it onto your xbox hardrive 2.go to your themes tab 3.go to change theme 4.select your premium theme 5.wala your theme should now be changes i know this works im using the black ops premium zombie theme
you also do the same methord to change your gamer picture but select change gamer picture in said of theme
You can also use horizon and make your own custom themes just by placing pictures in the tab section if you need help learning how to do this hit me up xACHILLIESx on xbox live.
the themes are only really good for viewing partys so if you have bought it you wasted your microsoft points