How do I do it? What tools do I need? Thanks
I just did this for the first time last weekend. Here’s a great site for repairs/maintenance:
hammer and a chisel… or a shimano lockring adapter, wrench, and a chain whip. Stand behind the wheel with cassette facing away. Put the lockring adapter on the lockring. Hold the adapter with the wrench in left hand ready to turn to the left. Wrap the chain whip around the cassette to the right side. Push wrench down to the left with left hand and chain whip down to the right with right hand. Lather, rinse, and repeat. Should cost about $20 or so in tools.
Hopefully that helps.
Thanks!