An ordinary easy out can also work. But if you have to drive the Torx or the easy out in, make sure you support that side of the frame; if you don't you will squeeze the frame and have a heckuva time getting it back in shape.
There are other ways you can go, based in part on whether the gun uses grip screw bushings and whether it is important to preserve the grip.
Once you do get the screw out, take the other three out and trash them. Go to either Torx or to a regular slot head; either is better than the Allen type.