If you mean from the app store you can't but If you mean from home screen you hold the app until it starts to shake then you press the x bitten and press delete. If the game or app was from the game center it will ask you do you want to remove this from the game center. That's your choose. Anyway after your done deleting everything you want to delete you press the home screen and then every thing will stop and be back to normal exepet for all those other apps.
iPhone- all you have to do is hold down on the application you want to uninstall the your apps will start to shake. Also there will be an x on the right hand side of each app simply tap the x and say yes to the "are you sure you want to delete this app"
Android- simply go into the market and under apps installed find the app you want to uninstall then after taping the app press uninstall