Whad'ya know, that's what my hubby does for a living. To get old tint off, use Windex with ammonia and take to it with a razor blade. It's a bear to get off, especially junky tint. Just don't use the blade on the rear window as it will severely damage the defrost lines. Use a non-metal scrub pad instead.
If you don't want to go through the work, take it to a window tinter. They'll probably charge by the hour to remove it.
Tint laws vary by state. Maybe you're not illegal??
and its a good thing u told me to not use a razor on the back cause i would of if u didnt tell me
so i think ill use that Jasco heavy duty remover shtuff on the passenger windows, and maybe try a steamer on the back (if we even have one,...grandpa might