They generally run fine forever.
But if you're looking for an excuse to pull em apart, they often have some play which can be eliminated by removing a shim or two, which theoretically should result in slightly better shifting.
Pull the cassette and spindle, then you should be able to see a couple of slots in the edge of the bearing cup. Use an appropriately sized bit of plate to crack it while the body's on the hub (it has a left-hand thread), then use a 10mm allen key to remove the cassette body from the hub. You should be able to continue unscrewing the cup by hand - do it over a rag. Grease is a requirement for reassembly.