Possibly you have a condition called Gynaecomastia, where you actually have breast tissue, like that of a woman's. If this is the case, then the only thing you can do is have surgery to remove this tissue.
If it's just that you're overweight and carrying lots of fat, then you just need to diet and exercise. Just do cardio exercise and a balanced weights programme. A split routine may be best, as you can exercise one or two muscle groups at a time and overload the muscle.
Try Flat & inclined chest / bench presses and inclined chest flyes. But make sure you work all the muscle groups at other times. The more lean muscle fibre you have, the more your body fat will be used as fuel.