How can I lose weight, and reduce the size of my breasts?

Low Fat Diet. Modify your diet to reduce your breast size. Since breast tissue is made mostly of fat, decreasing your overall fat intake could lead to a reduced bust line. Monitor your diet by keeping a detailed intake log. Assess each food group to ensure you're receiving adequate nutrition while attempting to reduce your breast size. Lose weight gradually to prevent breast sagging. No more than 1-2 pounds/wk.
So many ways. Weight loss depends on how much weight you need to lose. Bariatric surgery for morbid obesity, medical weight loss for obese or overweight. Proper diet and exercise can work, just difficult to continue either for a long time. Breast reduction would need to be done by a plastic surgeon, however with weight loss you may lose volume in your breasts.