Butt & Thighs!!

I want to know how can i make by butt and thighs bigger because my upper body is bigger but its not too big because i have really skinny legs and arms and a small waist but i have big boobs. So i want to balance out my body by getting a butt and bigger thighs but every time i do gain weight it would go to my stomach then go away or if it does go to my thighs it only goes to the top of them so my legs still look really skinny, help?