If it's water soluable, wipe if with a wet cloth, if not, try paint thinner. If the paint is dry...(which by now, I'm sure it is!!!), try using a utility knife blade CAREFULLY!
MAMAMAY SAYS: for water based paint if it is already dry then paint thinner will only smudge it around. Boil a pot of water on the stove, and pour over area. While that sets in boil another pot. Buy mr clean extra strength magic erasers and dip it into the boiling water and quickly scub vigorously in one small area while its hot. Redip and repeat.Where a glove to avoid being burned. A fingernail scaping on little tough spots works better then a knife blade. This is very time consuming but it is working for me slowly but surely. Nothing else has helped in my experience.