Try soaking the coin in distilled water for a few days to soften up the green spots on it and then remove them with a toothpick. If distilled water doesn't work you could try olive oil. Keep in mind you might damage the coin and don't know what's underneath so it might end up worse after cleaning.
As for value, this is a very common coin and would probably sell around 5 to 10 euro.
I collect and deal in ancient Roman coin. In case you're looking for affordable ancient coins or need any help with the coins you already have send me a message.