You probably really don't want a big butt, do you?? You want a small,shapely,tight butt. Try running, lunges, squats, and you will look better in your clothes.You need to exercise, or buy that "booty pop" thingy. ; )
You will need to have firm tight fitting jeans that have pockets at the back and high heels if you wish to make your butt appear bigger. You need to practice good posture and watch your weight by building muscles. Get more instructions on http://www.ehow.com/how_5395060_make-butt-look-bigger.html.