Download a memory hacking software like cheat engine or L.Spiro MHS.
Watch a vid on how to use it or read a guide.
Inject a bypass into CA
Open your memory hacking software at loggin screen and click open process and open engine.exe
go in game and search for address.
Start with a no reaload.
Look at ur ammo and search for that value, e.g 30
Then shoot a few bullets and click on the next scan and write in your ammo e.g 29
Keep doing this till you have 1 address in the box thingy.
Lock that address.
Play around, im going to make a fly hack once windows 7 installs and i only started this yesterday