It has to be removed from the car and scraped with a wire brush to remove the foam. You can pick up headliner material as well as the spray adhesive at your local trim shop pretty cheap. If they don't have the glue, check your local custom stereo shop, if not there Home Depot. Use the 3M Upholstery Adhesive. Make sure you spray it on both sides, then wait at least a minute before attaching it to the headliner board. It's not too hard to do, just sometimes a pain to get in and out of the vehicle.
Good Luck!
