You can start with a good detergent (Dawn dish washing liquid) and soft scrub brush and if that fails try 90% isopropyl alcohol, although for old dried fingerprints Tert-Butyl alcohol works. Then use a Retr0Brite solution of 12% hydrogen peroxide is a bowl of warm water for the yellowing; remember that once the are rinsed and dried from the peroxide bath to spray a coat of clear polyurethane to prevent yellow from returning.
Just a suggestion.
