OK, I have that exact pump and the diagram cleared things up very nicely. Just like the diagram illustrates, I was able to remove the plunger by unscrewing the cap (counterclockwise) where the plunger shaft goes goes into the pump. The cap is in two pieces, the hook part and the threaded cap. The hook has no threads and is secured by screwing the threaded part in, so twisting it will bear no results. You need to turn the cap, which is only about 3/16 of an inch thick when secured. Maybe some pliers will help. But be careful not to damage the soft material when doing so.