How to get the factory tinting off my windows?

I recently bought a 1977 chevrolet van, its actually in great condition and its been well taken care of but the tinting on the windows is bubbling up and its wrinkling up all over the place I guess as old as the tinting is its to be expected but I would like to remove and redo it I tried scraping it off with a razor blade but its as if the tint and the window are one entity now, not sure if that has something to do with it being factory tinting or what but I cant scrape it off, any suggestions would be appreciated thanks so much