If it's the head-lining you're on about, it helps if you heat it up with a hairdryer as you peel it back. When it's cold it gets brittle and tends to just rip.
If you're talking about the plastic roof strips outside the car, the front clips push forward and lift off (be warned, they're stubborn) then you need to CAREFULLY pry the main strips off with the old fork-tounged pry-bar. But put a cloth under it so it doesn't mess up your paint.