It is a good idea to first of all test it on a discreet area of body work where it does not matter if it does fade the paint. This is unlikely to happen but it is best to do a tester to begin with. A tester can be done somewhere such as the inside of the door. Begin by applying a small amount to an old rag and gently dabbing it against the paint. Wait a few hours to establish whether there has been any negative effect to the paintwork and if not you can carry on with the rest of the vehicle.
Paint thinner is often used to remove oil based paints or to remove contaminants or scrub marks. Paint thinner is extremely flammable so ensure you keep it away from the engine of the vehicle and be careful not to spill any. You should also be careful not to get any of the paint thinner on yourself. Follow the directions on the packaging as incorrect usage can irritate the eyes and skin, damage the nervous and respiratory systems, and cause kidney failure. Protective clothing, including gloves and eyewear, should be worn when handling this type of paint thinner.