A.F.
Depending on how the snap is made, if you look into the hole the snap snaps into (usually on the front flap of the pants) sometimes there are two little metal "bars" that go across the inside of the hole to "grab" the snap and hold it in place. You can take some small pliers and pry those apart a little to loosen them and that should help. If the snap doesn't have those, and is just snapping into a hole, you can try the same technique but on the actual metal, or you can squeeze the part that snaps into the hole to make it a little smaller so it will fit better. You have to be careful not to do either way too far or you might make it too loose so it doesn't stay closed. Hopefully that made sense... It wasn't the most eloquent way to explain it...