How to create Multiple Themes Skins for iphone apps

Question

I already have an iPhone app that the app store has authorised. I now want to design many themes for my app. Can someone please give me information, links, or instructions on how to make themes for my app?

For the Boys, I want to make a Metal theme, and for the Girls, a Pink theme. Again, by theme, I mean that the features and functionality of the entire app will remain the same, but the user can select the theme they want to view based on whether they are a boy or a girl. Additionally, just the graphics, backgrounds, and music will alter when the theme is changed to reflect the applied theme.

A big thank you!