Car window tinting...?

I have a 1979 El Camino, one of the previous owners had a purple shade of window tint put on, it appears to be a film or thin sheets of transparent plastic on the interior and exterioir probably done in the 80's, I was wondering of any techniques to remove the sheeting, it's bubbled in several areas and can be peeled away...but appearently another or the same owner tryed to latter remove, and scratched a bit of the window, so I do not know how it should be removed, also, I was thinking of not simply removing but replacing it...so any tips on instalation would be helpful, thanks in advance.