It should be an "O" ring on that top cover. You need to remove (or at least loosen it initially) the adjustment nut first, while holding the adjustment bolt from turning. Then remove the lock ring holding the cover. After that it, remove the nut and run the adjustment bolt in (clockwise) to raise the cover out of the housing and off. I would count exactly how many turns it takes to do that, or, you'll have to go through the adjustment procedure to get the end play clearance right.
