if you eat the right kinda of carbs and proteins and do a lot of squats and lunges and balanced cardio, you can focus on your butt muscles and make them larger. good carbs are things that aren't over-processed, nothing with white flour like bagels, cakes, white breads, crackers, and no white rice, or pasta. if possible, avoid food with gluten. eat lots of lean protein like fish and white meat chicken, and cut out excess sugar.
you can't choose where you loose weight, but you CAN choose where muscle is added, but it takes a lot of patience.
it's mostly based on genetics. and having a ghetto booty does not equate to a weight problem, sometimes its just about body type. I have wide hips and a very curvaceous figure/rear and yet I'm still on the low side of average for the bmi of my height...i wear extra small tops, 34C bras and a size 4 or 6 in jeans and people say I have a ghetto booty...but I am by no means fat in fact once my aunt thought I had an eating disorder just because I am so tiny. genetics are what really determine the difference between a curvy shape or a flat ass.
Well there was a model on tb who's butt I wish I had and she said she got hers by going to a nutritionist and getting on a healthy high carb diet and while she was doing that she done squats and crunches and lifted weights to keep the rest of her skinny while her butt grew.
Then you could always get some kind of hormonal shot...but I don't really know anything about that. Needles frighten me so I didn't care to research it.