In a first level, the proper resolution modes must be defined in the Screen section of your /etc/X11/xorg.conf file.
Fedora's installation wizard might have successfully detected and defined these. In this case:
a) If you are using Gnome, you can switch from Gnome Control Center (if you don't find it in any of the menus, issue "gnome-control-center" in a console terminal)
b) If you are using KDE, you can switch from the KDE Control Center (if you don't find it in any of the menus, issue "kcontrol" in a console terminal)
