My 1990 coupe deVille needs a new vinyl top. I found one for it at a junkyard in superior condition but before I go get it my question is ...how do I remove the old one?

Second question is.... how do I remove the one on the junked car? I don't want to damage a damn fine looking replacement.

Would all this require taking down the headliner because the vinyl shell is screwed from the inside? Or is it an outside tricky-trim thing?
Any special tools required so as not to do damage?
Being more specific, the cabriolet vinyl top on my car is half the roof, and the replacement I got my eye on covers the coupe full roof.
It's not glued on, right?