There are 2 methods:
Slow release - gradually turn the programme selector to the steam position. This is used for stews, vegetable, joints of meat and fish dishes.
Fast release - place the pressure cooker under a cold tap directing the flow of water onto the metal part of the lid. This is used for liquid based dishes such as soups, rice, pasta, milk puddings, egg custards, cake and pudding mixtures, recipes containing rice or pasta and recipes with a high liquid content, in order to avoid the liquid shooting out of the steam valve along with the steam when you release the pressure regulator valve.
When the pressure indicator is down, all pressure has been released.