Repair. How do I get wheel hub off to change wheel cylinder

If it's the "Full Floating" Axle I think it is, you'll need to remove the 8 bolts holding the axle in place, remove the axle and then remove the large jamb nut, retainer, adjusting nut, washer and outer bearing. Sometimes the retainer can be a challenge - it usually has tabs that will need to be bent away from the nut before you can remove it. You will need to pack the bearings with grease before you put it back together or you'll end up destroying one or both spindles. Yes, there is gear oil - no, it does not bathe the bearings. Don't forget the wheel seals. Use the good ones.

BTW - change both wheel cylinders, brake shoes (be sure to measure them or bring them to the parts store with you - there are different sizes) and flush the brake system. Check your hardware thoroughly. I know, PITA - but you won't have to mess with it again for a very long time.