Hi jimmonas
I assume that you have a key to fit the side of your radiator. You insert the key into the opening, usually at the right hand side of the radiator and turn anti clockwise until the air is released. You should hear the air pressure reducing. Make sure the radiators are turned off, or you may well burn yourself. Place a jug or basin underneath whereyou are bleeding them to catch the water. Turn the key clockwise to shut off the valve. You should have nice and warn radiators after that. You might also get a bit of dirtty water while you are doing this.
Good Luck.