Hi there!
While the nipple size is genetically determine and cannot be changed; if you are aiming at losing weight, it is important to calculate your current BMI and the target BMI. The target BMI should be in a healthy range. Aside indulging in moderate amounts of physical exercise it is also essential to maintain a healthy diet plan. A healthy diet should consist of adequate amounts of calories with carbohydrates, proteins, fat and plenty of fruits and vegetables to supply vitamins and minerals. Skipping any of the food components is not considered healthy. Also when aiming at losing weight the protein intake may be slightly increased and the carbohydrate intake slightly lowered. The calorie requirement should also be adjusted for ones physical activities as well. Lower than adequate calorie intake can also cause weight gain, due to the stress hormones kicking in. Start with a healthy breakfast, moderate lunch and light dinner. Also keep a track of calorie intake and your work out. 0.5-2 pounds a week is decent weight loss. The weight loss may be slow initially due to the muscles building and would gradually gain pace. With gradual consistent efforts, you should be able to lose weight as desired in a healthy way.
Hope this helps.
Take care!