Window tint is REALLY annoying to remove. Best bet? Wait for a very hot, sunny day. This heats up the tint, and makes the adhesive softer.
The ease of tint removal really depends on what brand the tint is, and in what condition it is in. I got lucky, and this window tint peeled right off without much difficulty.
I will also detail another method that will work much more effectively on a rear window with defroster lines.