Anyone know how to change NAT type?

my friend has said you just have to reset network settings, is it that easy? i play on a strict NAT type. when trying to play cod im stuck trying to find games, only finding foreign games. i have turned on. off my router many times... can anyone link me somewhere to disable the UpNp thing, as the xbox.com site is no help at all. i need to change it as i cant find any games. thanks in advance :)