Step 2: Removing The Valve
There will be a retaining ring ( not pictured) just under the upper lip of the opening. You can pry this out with a small screwdriver or something similar. Grab it with a pair of pliers and get it out of that lip.
Now it just needs to be twisted counter clockwise a few degrees to come right out. Put your screwdriver on the tooth pictured and tap it with a hammer. This should twist it slightly, allowing you to lift the valve right out.