There are several ways to remove the tint, depending on which window. I believe that you can just use some good, new, razors on the side windows. If you want to keep your defroster lines in the rear window, I'd follow the instructions at
www.tintdude.com
I just did this last weekend. Take a blag trashbag, place on outside of window and using the razor, cut to the general shape of the window.
Douse the inside (tint) with Formula 409 from a spray bottle and "stick" the trashbag to it. Basically the trashbag will keep the 409 from drying off and the bag will stick to anything wet. Leave it facing the sun (hot sun.. maybe ~80 degress), for about an hour.
Slowly try to peel back the tint (uses a razor or fingernail to start it), while keeping the trashbag in place. If you pull off the trashbag, the remaining 409/tint will dry while you work on one section, and you will have to start over.
Many times, you can pull all the tint off in one pass, but like in my case, I had to make several passes at pulling broken off pieces out. Good luck!
Try also running the defroster and heat in the car... should make it much easier. If you can rent a steamer, that will do the trick as well...