Summarize:

Press the jelly around the edge, using your finger. Gently pull away from the edge around the whole jelly. Place your hands over both the base of the plate and the base of the mould. Shake quickly and sharply and the jelly should release.
Fill a bowl with hot water. Dip the jelly mould into the hot water three times. Place on a firm bench. Turn the jelly mould onto a plate. Finished.