To change skin ingame type: settings and change the public ct and public t model to whatever you like. If you want us to add a special skin just go to the forum and write it there somewhere.
We have 4 different |VIP| skins that only donators can have. Check out here to see how to get them: http://www.zombiesfromhell.net/index/0-7 We will add more |VIP| skins if people donate and want more skins!