Entering cheat codes on quake 4 on xbox 360?

i am looking for detailed instructions on how to enter the cheat codes for quake4 on the xbox 360.this is the code,it says enter B, A, X, Y, left, right, left for the Ammo Refill. now what im asking is, when do i enter this? is theri a special screan? or place i need to be. and am i suppost to use the sticks or the d pad for the lefts and rights? i cant seem to make them work. please send me step by step instructions. thanks alot for your help!!