Remove the tinting film from the window per manufacturer directions. One way to remove it is to spray the side with tint with a window cleaner containing ammonia. Then, cover it with a plastic trash bag or dry cleaning bag. This only works if the window is in the sun. Wait at least 45 minutes, peel off the bag to remove the tint. If necessary, reapply the window cleaner and another plastic bag to remove more of the tint.
Scrape off the remaining film carefully with a razor blade. If you are removing the tint on the back window of a car, do not remove the defrost lines, if applicable, with the razor blade.
Scrub the window with soapy water. Use a nylon scrubbing pad, testing it first in an inconspicuous area to be sure it does not scratch the glass. Otherwise, use an absorbent rag, such as terrycloth.
Moisten a rag with paint thinner and scrub the window to remove the remaining tint film glue. Continue until the window is no longer sticky. Concentrate around the edges and corners. If you are going to have the window re-tinted, you must remove all the adhesive first.