It's really easy. You just need to open the door and you will see how it twists off. A flat headed screw driver will help you unsnap the piece that locks it in place. Should take you less than a minute to do.
No, there aren't any screws to remove. It twists off. But a slotted screw driver will help you get it started. There are notches on the piece of plastic that the fuel door fits onto, once you have these notches unhooked you can twist it right off. If the cabrio is different, I'm not aware of it.