Leave the car out in the blazing sun for an hour or so, Then use a razor blade and start at a top corner.
Peel the tint slow and at an angle, That will keep the tint in big strips while removing.
Once all of the tint is off, You can use Goo-Gone or just take some Windex with a razor blade and scrape just the glass until the glue is gone.
Just make sure you have a few blades handy.
After using 1 blade for 5 minutes w/ the glass cleaner, it'll get dull fast which will make the process turn difficult, Change blades and begin again.

Your last resort, Take it to a tint shop and let them do it, But expect a $35 charge if not more.

Good Luck
-Jeff