1. First, pop out your Crysis disc or exit the Crysis game via the XMB if you have the game on your HDD.
2. Go to your game collection or favorite local game store.
3. Look for a case that says "Killzone". (There is usually a number 2 or 3 after the Killzone label. It does not matter whether you pick up 2 or 3).
4 Pop the Killzone disc in your PS3.
5. Voila, you can now enjoy the best FPS graphics on any console
You're welcome