Yea pretty much what he said, take the stock h-pipe off and bash all the catalist out with a wooded pole and a hammer or something, just watch out for the 02 sensors if you have em. Or just pick up a cheap o/r h-pipe.
Edit: if you mean how do you take the whole pipe off it unbolts up near the headers/manifolds and down at the talipipes, it might be somewhat rusty could take a little work to get it knocked loose.