There are quite a few headlight restoration kits that work. Basically, they rub down, then polish and buff up the surface of the lense. Other people have done them using progressively finer grades of wet and dry, and finishing off with compound applied with a machine polisher.
The problem is, is that the UV protection layer has broken down and gone cloudy and yellow. By restoring the light, you will remove the remains of the protection, meaning the bare lense underneath will go cloudy and yellow.
