Normaly, going full screen is controled by a setting of the games themselves.
All games should have some options or settings screen available. The exact location and terminology depends on the game you use.
It's also possible that you are realy in full screen mode, but the game's resolution is not correct.
Here also, you should navigate the options and settings of the game to set the desired resolution and chose one that match the native resolution of your screen as closely as possible.
Electro, September 2011