1) Disassemble them as unscrewing the cones' contra nut and the cones themselves.
2) Wipe the old grease with something ( I am doing it with toilet paper )
3) Wipe every individual ball of the hub.
4) After everything is clean, put some grease on the hub's ball beds.
5) Keep doing that till you do the entire circle.
6) Pick up and place every one of the balls back on, so they can sick into the grease
7) Put the cap back on.
8) Screw the cones !! BY HAND !!
9) Screw the contra-nut back on to hold it in place