Is it possible to lose breast weight (decrease their size) and how?

Yes but.... When you lose weight you do not have control over what parts of your body lose over others. A healthy and diet exercise program will cause weight loss throughout your body. If your breasts shrink too much, talk to a plastic surgeon about your options for breast enhancement.
Yes. Healthy diet and exercize can lead to weight loss in male breasts. Sometimes however, male breasts have abnormal glandular tissue that is not responsive to weight loss.