It depends on the type and the position of scratches. If there is a just scratch aroused by dirt or dust and the scratch is just make the lenses obscure, it is easy to remove. Put some toothpaste on a piece of cotton cloth and wipe out the scratch with it. Then, rinse sunglasses under the tap. Spray special detergent on it and dry the water on it. Don't wipe at the last step. Then, for a more complicated situation, the recovery will be harsher. If sunglasses are scratched by some objects with sharp edge, such as the situation can be terrible as the scratch is done on the surface and irreversible. If the scratch is on the frame, you can go to a glasses store or factory. They have polishing machine and could polish the frame. But if the scratch is on the lenses, they won't polish the lenses as it will thin the lenses and the function of sunglasses will be destroyed. Thus, the scratch on the lenses can not be removed.