The best way to lose belly fat with your BMI is to burn fat. You can do this by eating lean meat and raw fruits and vegetables. You should also do some specific exercises such as crunches and aerobics. Taking Amino acid supplements will also help in cutting down belly fat.
When reducing, body fat is lost in general. You can't target fat loss in a specific area. When I lost a lot of weight, my shoes were too big and I had to buy some smaller ones (for example). You can tone abdominal muscles to lessen belly sag.