It depends on what's causing the staining. If its an extrinsic (outside) stain, then bleaching or a dental cleaning and polish could help alot. If its intrinsic (inside) bleaching may make a difference but it could also be that your teeth are naturally more yellow. The only option to completely hide the discoloration is to do veneers, which are thin pieces of porcelain that are bonded to your teeth and hide your color.
Is it ok to bleach a 13 years child's teeth
13 years old is kind of young. Is it a major cosmetic issue? How about a dental cleaning?