That is not a standard fixing. It should be just a simple bolt with a socket head, which you unscrew while holding the propeller fixed, usually by jamming with a wooden block against the hull. The screw comes out, unscrew the cone with a bar in the hole and the propeller slides off the splined shaft. Think you will have to lock the two inner nuts together so that you can undo the screw. Note that there should be a plastic washer, it is important this is replaced. When the prop is off the anode is held onto the housing with two cap screws.
Replace in reverse order and when the cone is tight insert the long locking screw and do up tight. suggest you replace it with a new one - the Volvo one has a locking adhesive inserted in the thread or you can use loctite.