Dawn dish soap and a razor blade. Mix it in a spray bottle. Try to peel back a corner at the top, or use the blade to get a section at the top to pull back, then spray the soapy mixtre in there and let it work. Slowly pull tint away and keep spraying the entire windows to let the soap mixture work.
I've also heard of using WD-40, ammonia, 409, or oven cleaner for tough cases