Hi I think you can ,now that it is off the hub have a look on the outside edge and there should be a seal , which you can prise off. This should expose a screwed race which can be unscrewed anti clock wise ( lh thread) there will be two notches or indents which will allow a punch to unscrew the race. Inside you will find 1/8" ball bearings on both sides and a set of pawls that engage with notches to drive the wheel forward.
You will now have to hold the cassette body in a vice the do the job use two strips of wood to protect the body from the vice.
There are a lot of bearings and they are loose. When replacing them fill the race up full and take one out imbed them in a light grease to stop them going all over the place....of course clean all the surfaces before replacing them. There will be some shims which allow different settings to take up any wear, you may have to discard one to remove any slopiness when tightening up again. It really doesn't matter if there is a little looseness when reassembled as you will now have new bearings.
The same proceedure goes for Shimano... a lot of bike shops wont repair them because of the work involved and would rather sell a new unit....some bike shops also don't how to do it.
My 7 speed cassette began to develop a knock only when using the 5th gear and cruising around 24km/h. Had me puzzled for awhile what was causing the knock until I found the cluster was quite sloppy. Removed the thin shim and refitted the bearing cone and no more knock.
So there's a possible thing that can happen if the cassette is too free.