The easiest way to do it is to use some Simple Green. Hear me out as I know what I am talkin about and have done it plenty of times before. Get a bottle of Simple Green and 2 large garbage bags. Spray the back window down with the Simple Green(soak it) then, place the bags against the window so they cling to it. Leave them there all day in the sunlight or overnight. Then, just grab the corner of the tint and most of it will come right off. You can get the excess with a brillo pad and windex. On the side windows just grab the corner and pull until it all comes off in one piece, then spray windex and scrape the rest with a razor blade.