There are surgical procedures where they insert butt implants to enhace your behind and you can also have fat injected into your butt from other areas of the body. Butt implants are the most sought after surgical procedure in Brazil, and if all else fails it can be a good way to get the shape you want. But with every surgery there are risks so make sure if you are considering this option you do a lot of research and get a doctor with impeccable credentials.
There are also non surgical ways you can try to build up your butt. Your butt is comprised of large muscle and muscle can be enhanced. I know there are some workout videos specifically designed to enhance the butt, I think one of them is called the Brazillian butt lift you can look for it online I'm sure you will find many. I would definitely reccomend trying a more natural method before you opt for surgery.