I've died shoes before, and had much more luck with the powder than the liquid. But even with the powder the soles don't dye that deep; the dye shreds off after a session or two in high contact areas.
I'm guessing it will be similar with wheels, which are presumably less absorbent than rubber soles; you can dye the sides but the edges will probably wear back to whatever color they were originally.
As for the dying process, all you have to do it heat water to just before boiling, pour the water into a bucket or whatever, add the dye (preferably the powder), mix it up with a stick or some such object, and drop in the shit to be dyed. Stir it around for a bit. The longer you leave them in the darker they will get. Repeat the process if they come out too light.
It may be more effective to add the dye to hot water on a burner still, and dye shit in a pot with continued heat, but it will apparently ruin the pot you're using so I never tired.