R,
If the stains are not very old, you can get rid of them by wiping with dish washing liquid. (Use a soft sponge not scrotch brite or anything corrosive)Wipe dry with a paper towel.
If the stains are old, easiest way is to use magic eraser (Mr.White). If you have patience and time to try out, you can try applying a paste of washing soda or baking soda and after some time, scrape it off and wipe with wet paper towel.
Magic eraser works like a charm.
CI.
