It is not possible to polish spectacle lenses to get rid of scratches without altering the power of lens, as a result it would be necessary to purchase some new lenses.  It is possible to protect lenses from scratches by adding a special coating. When you ask for your spectacles to be reglazed (or think about buying new ones) ask your optician about a scratch resistant coating on the surface of the lens. This coating will help minimize any future scratching and enable you to keep your lenses for a longer period.