The answer might seem simple, "You have to burn more calories per day than you consume." "Great! How do I do that?" Well, that means that if you get your body moving more and eat slightly less calories your body will slowly, but surely begin to start burning off stored fat as energy.
Also, your belly consists of two basic types of body fat. Subcutaneous fat (the stuff you can pinch at your sides) and Visceral fat (deep abdominal fat the sits beneath the muscles of your abdominal wall). Having higher than normal body fat percentages can pose increase health risks. Ask your doctor or a local fitness professional to conduct a body composition screening if you need an assessment.
Research has shown that weight and resistance training on a consistent basis will help to decrease the stuff you can pinch at your sides and arms, but not the visceral fat underneath the belly. No, that doesn't mean that if you do a lot of weight training exercises for your abs that they will, in turn, get ripped. Your body burns fat from all over, slowly, over long periods of time. Research has also shown that cardio interval training is the best method to help decrease visceral body fat, but not subcutaneous fat. Interval training can be described as performing short bursts of vigorous cardio intensity (something that makes your heart beat hard and your breathing escalate) followed by a period of low to moderate intensity (a pace where you can catch your breath). Do this interchangeably for 15 or more minutes and you got yourself an interval workout.
For the best body composition change results, research has shown that participants who incorporate both types of exercise into their weekly routines achieve the best fat loss results. This is compared to participants who only did cardio vs. participants who only weight training vs. those who only modified their diet and performed little to no vigorous exercise.
The research is out there. People who find ways to include modifying their calorie intake and implement cardiovascular and weight training exercise into their daily routines, consistently show the most progress getting rid of their body fat.
Every person is different. I recommend that you meet with your doctor, a certified fitness professional, and possibly a registered dietician to help you figure out the right mix for your body. This way you will have the right combination of health information, exercise, and nutritional recommendations for your body type.