Try taking the smallest cog off alone. Use a flat screwdriver and gently pop it off. Do the same for each of the following cogs. In some cases some of the cogs will be riveted or screwed together. Those will have to come off together.
Once you have all of them off you can and should fill down the burs on the cass body if there are indeed some causing the hangup.
Use a rubber hammer and a pipe to hit it off. Hub came with it.. Once I got the hub out I cleaned and rebuilt the hub. Found the bur that was holding every thing up and filled it off. New cassette is on and works great.