the "thing" the sporocket it on is called the sprocket hub......it is easy to take off.......take wheel off...then wheel hub on end of axle....take off two axle nuts and that will slide off......you can also take sprocket off of it with the six nuts that go around it and you will just have the hub
the swing arm bearings just slide in where they are.....take the chain off,,,,,,,,,loosen the big bolts that goes through the frame and swingarm.....may need negotiation to come out....be sure not to bust up threaded end of bolt..............then swing arm should slide out......take off dust caps on each side.......there is a spacer inside the swingarm that the bolt rides in.....you need to get that out and the bearings are on each side behind the dust caps..you will see them...you can find a long screwdriver or punch and bang those out.......put spacer back in...throw in new bearings.....grease them up.......and back in it goes