Is there a way to remove scratches from glasses and sunglasses?

Usually not: Sometimes glasses can be buffed but generally, scratches you can feel with you fingernail means the lens needs replacement.

Not really: Next time you get new glasses, you can ask about which material for the lens is most scratch-resistant and/or adding scratch-resistant coating.

Sometimes: If the plastic lenses have very fine superficial scratches, an optician can often buff them out for you. Check with a reputable optical department and have then inspect the lenses to determine what can be done.