Plastic shut off valves

I have plastic shut off valves on both my bathroom sink and toilet. The lines are attached at the valve by some compression fitting that can't be tightened or removed and of course leaks! I've got new valves/lines to replace these but I don't know how to remove the plastic valves. There is copper pipe coming out of the wall and there is about 1/2 inch sticking out so I could hack the old valve off. Any suggestions? Thanks!

valves

Try twisting them while pulling on the valve. Otherwise break the valve apart so you slide the toothed ring holding it, off the tubing.

Be sure you turn off the water first or you will look like this

When you say "lines" ... are you talking about the supply line going to the sink and toilet? Or the copper water line going to the valve? I'm picturing gray Qest brand valves.

Thanks for all the help. The lines I mentioned were the supply lines. The plastic valves came off really well until the last one! Just when it seemed easy!