Wayne, for goodness sake. Body structure often related to cultural origin - you may note that e.g. Caribbean women have large buttocks too. Personally, as the owner of a large bum, I would do anything to reduce it rather than make it larger. You would have to buy differently cut clothes, and so on.
If you are going to do it, use a private medical facility who has a reputation for plastic surgery. Use a back street person, you could well end up with septicaemia.