You have to burn more calories than you're eating. You can go on certain fitness websites, enter in your BMI and what your goal weight is and it will tell you how many calories you need to be eating

That's actually a healthy body fat percentage. I'm 5'1" and when I was in high school, I was at 33%. I took an aerobics class within the school and the teacher helped lower it to 22% she said anything lower would be unhealthy.