Log on to your pokemon global link account. On the bottom right corner of the screen there is a Red Coded DS with the word "Customize". Click that. Under the C-Gear skin simply click on thePokemon of your choice. Of course you have to use your code from your the Pokemon Black and White: Official Unova pokedex and guide to even get the skin you want.
There Is A Link With All The Downloadable Theme's
I love Weird things ¯(°_o)/¯