Boil N Pop always works for me.
Basically, I grab a pan, fill it with water, and toss the parts in that I wanna swap. Turn up the heat and then mind the parts so they don't touch the sides of the pans. You want to wait until tiny bubbles form all over the parts and when the water starts to boil just a little pull them out.
Be careful, as the parts will sometimes have this hot water inside of them. Also, they cool quickly so just suck it up, schoolgirl.
Anyhoo, it's simply a matter of applying pressure from there, boss.