Make a hole and put a crow bar or claw hammer behind the sheet and just pull it out. That is how she did ours but it was messy. Be careful you don't pull any electric cables behind the walls.
Use a crow bar to break through and then remove the screws from the pieces left on the wall. Be careful of wiring and pipes such as plumbing.
I say lay a drop cloth and take a hammer to it, lol
Do you want to take it down with the intention of re-using it again, or do you want to completely demo/trash it?