"tintoff" is available at wal-mart, parts stores, etc...even "goo-gone" will work. Spray or wipe it on then press saran wrap up against it so it won't evaporate...let it sit for an hour so it can be absorbed then peel off the tint.
Ammonia doesn't do much to the adhesive but does a fine job turning the tint purple. For windows with defroster lines i'd suggest a steamer
worked fine on my tint that I didn't mean to take off on my old car HAHA