It is better to remove the old tinting because it will not be able to stick to a new one. According to the law, it is allowed to tint the front side windows, provided their degree of light transmission will be 30-35%. Still, this degree of tinting will be very difficult to drive at night. I have the front windows that are not heavily tinted, and I decided not to tint the rear. To protect my child from ultraviolet light, I bought a curtain here http://snapshades.com.au. This curtain is very comfortable and does its job.