Step 5: Gently pry back the diaphram.
The black rubber diaphragm is currently fit snugly over the blue plastic circle, which is the gasket cover. Gently pry the black rubber off the gasket cover. Once off the whole thing will fold back like a door on the metal arm it is attached to. Be careful to not rip the rubber but it should be fairly easy to remove.
Note how everything is oriented. You will need to remember how that blue gasket cover is positioned when you reassemble the parts. I look at the part that looks like a little arrow facing up.
We will have to do this for both sides, so note all these steps for the other side as well. On the other side it's as if everything is rotated 180 degrees so on the opposite side the arrow on the gasket cover faces down. You can do both sides at the same time or first one then the other. Whichever you find easiest.