pull it off.. strip it down completely (I like using a wire wheel on a drill). If painting I prefer to use a primer first.. a few coats of primer will help alot..
Next get your favorite color of high temp paint (caliper, engine, or whatever u can find as long as it is high temp). High temp paint will last much longer then standard paint.. yes standard paint will be fine however u may end up doing the job again next season.
Paint the cover with a few coats.. and then clear the cover with a few coats.
bolt back in with a NEW valve cover gasket and enjoy the look.