Passionfruit, When to Harvest

I don't know when my passionfruit is ready for harvest. Could you tell me? This is my first experience with the fruit.
The fruit on the plant at the moment is green and quite large please tell me what will happen from here. Do I have to pick them? Or, will they drop themselves?

When passionfruit (Passiflora edulis) is ripe it will be purple in colour. Other species may turn yellow or orange. The fruit also becomes softer as it ripens and develops a bit of a pleasant fragrance. Pick it at that point and enjoy.