DON"T just wack it with a hammer/punch...you stand a good chance of snapping your body/trigger guard if you do that.
Use either a proper pin punch (the punch is cylindrical and not tapered like a finnishing nail punch) that is the right diameter. Since I can never find mine
...I usually end up using a cut off allen key.
Place a piece of soft wood (i.e. pine) under the trigger guard. Or a piece of hardwood with a hole drilled in it. This will be the backer that supports the trigger guard as you punch out the pin. Be sure that the trigger guard is laying flat on the backer...and that the body/etc... isn't touching it or the sturdy surface you're working on. The punch needs to be a good fit. It CANNOT be too small or you're just going to drive it into the center of the roll pin.
Some roll pins are tapered on both ends...some are just tapered on one. Take a close look...obviously, drive it out in the opposite direction it was put in.
Align your punch and give it one sharp tap with a metal hammer (not a 20oz framing hammer, not a rubber mallet...a 10oz finish hammer or a regular 16oz hammer works well). If the pin moves...you're good. If it's really stubborn, check that your punch is really big enough, that your backer is fully supporting the piece, that you're properly aligned...and hit it harder. It should move. If it doesn't...turn it over and try hitting it from the other side.
A little penetrating oil might help.
If it's really bad...I've used a socket as a backer and a punch (it was a cut off allen key
) in a wood block. I juggled it all into a vice and sqeezed the pin out. A royal pain in the ass...but it works.
Use a backer when you're putting it back into your new receiver. Work on a solid table/bench. File the ends of the pin so there's a taper and no burrs.
Best of luck...