You can reduce your breast size by increasing your cardio routine and include weighted workouts as well in your weekly routine. Eating clean & healthy will help you achieve results quicker. I have personally found this to be true. It does not happen overnight however if you are consistant in your workouts and eat clean (no fried foods, alcohol, & eat smaller portions) you could see a decrease within a few months. Books that have helped me:
Tosca Reno - The Eat-Clean Diet
Dr. Peter J.D'Adamo - Eating Right 4 Your Type.
Best Wishes,
Rene'