There is a steel o-ring that is holding the drum in place. You have to take the swingarm apart to get the drum enough room to remove the ring.
Take off both wheels. On one side there is a sprocket. Remove the sprocket. and everything on that side. Then push the axle through the swingarm. That should push the drum off of the brake pads. Use a rubber mallet to hit the drum and make it move back towards the brake pads. You'll see the ring. Pull it out then the drum will come off.
Replace what parts are needed and reassemble.
Sorry I couldn't have been on here sooner.