thx a lot man. dats funny cuz i'm goin from 10 to prob 20 or 35.Get a trash bag and cut it to fit the window. Spray some water/ammonia mix on the window and put the trash bag cutout on the inside of the window. Let it sit in the sun or hit it with a heat gun from the outside. This loosens up with glue. Then grab a corner and pull. It should come off leaving little to no glue behind.
I did this when I went from 35% to 15% on my side windows and I didn't have to use a razor at all.