Get some razor blades, "000" or "0000" steel wool and lots of windex and patience. Start at the edge of the window with the razor blade and lift the corner then carefully pull and work at the edge with the blade.
If the tint is in decent shape, it should come off in one piece, ithe the tint is old you should be in for a fun time. After you get most everything off, use the wet steelwool to scrub off any excess.
I've never done this myself, but have watched my tint guy do it several times.
Good Luck!