If you've found out that your cassette cluster is loose or is getting stiff, it may be time to replace your freehub body. In order to do this you'll need to make sure you have all the right replacement parts and 10mm allen key.
Before attempting to do this, you'll also need to remove your cassette, axle, and bearings. Once those have been removed, it should be smooth sailing from there. Check out the video above for more information and good luck!