Thinking back to my detailing days... (wow, that was a long time ago)
I believe we applied a soap/water mix, letting it soak into the tint to help soften the glue, then used a heat gun (fairly low setting) and peeled it off, continuing to keep the tint moist. If possible, peel off in large sections, and apply soapy mix between tint and window as you peel it off.
Make the soap/water mix with warm water and enough detergent so that it doesn't drip too much, since you want it to be able to soak in. you'll probably want to apply a few times before you break out the heat gun. Ammonia or an ammonia based cleaner will work, too.
A razor blade will be helpful, but make sure to keep it very clean/sharp, and if you care about having a defroster, stay away from the lines (kind of obvious, I guess). If you must scrape near the defroster lines, gently/cautiously scrape towards them at a 90* angle.
I did a quick search, and it appears that I'm not too far off...
http://www.wikihow.com/Remove-Window-TintHope this helps.
Good Luck!