You can take it to a taxidermist and they will do it for you. Or, you can get a steel drum and a propane burner and do it yourself. Basicly you put the skinned head in and fill with water to just below the antlers, turn up the heat and let the water get hot. I don't like the water hot enough to boil but dang close. you can buy some caustic soda to put in the water and that will help break down the tissue and grease. this can be bought from a taxidermy supply magazine. Then, just let it cook for a while and periodically pull it out of the water and scrape of flesh that will start peeling away from the bone. get a wire coat hanger and make a hook on one end, stick this in the skull and scramble the brains. This will help them come out easier. You will need to add water once in a while to keep the water level up. keep cooking and scraping until the skull is clean.
When it is clean paint a mixture of calcium carbonate (get from taxi supply) and hydrogen peroxide, mixed to a pancake batter consistency, on the skull and let it set for a few days to a week and then just wash it off.
That is the way I do it. somebody may have an easier way (such as beetles)to clean them, but this works pretty good.