Hi, well, if you do in a terminal:
su -c "yum remove kmod-nvidia"
that's a start. Installing that driver also blacklisted nouveau so you have to:
su -c "rm /etc/modprobe.d/blacklist-nouveau.conf"
su -c "rm /etc/X11/xorg*"
to remove the xorg.conf file and other remnants of the nvidia setup.
Then all you have to do as reboot and you should be back into nouveau.
You can copy and paste those lines into your terminal, but if you decide to just type them out, just make sure that X11 is a capital "X", everybody makes that mistake.
BTW - if you decide to reinstall nVidia drivers, ask and we'll tell you the steps you need to do it successfully. It takes more than just installing kmod-nvidia, because Fedora ties it's kernel so close to the nouveau drivers.
Any questions, just post back, especially if your uncertain about anything. Also, you should type and execute all commands before rebooting, or else you'll get a black screen.