easiest to do is doing the sides like the read...
however, the sides you can scrape off since there isn't any lines to worry about. just spray some ammonia and get it really wet... then with a utility knife just peel up a corner. From removing stickers, wallpaper, etc, its best to form a sharp angle when you are peeling.
what I mean is don't pull the fil straight up (away from the window) at a 90 degree angle. peel it back over the area you have left, like if you are folding a piece of paper. This is a much better way to peel stuff and it should come off easy. If any part gets stuck, respray and with the knife, unstick it...