i don't know fedora at all. May be you can transfer my knowledge from opensuse. At the login screen there are 2 menu items at the left downside, where you may select the desktop kind.
Keep in mind, that you can do so only then when you have installed all the kde components.
Hope this helps.
[edit] Your question is more from a fedora question then from a kde question. May be you get better reactions at
http://forums.fedoraforum.org