How much will my breasts shrink?

I'm 19 and barely just go to a 34B, I was a 34A before. I'm trying to lose weight to be more toned and I currently go to the gym about 2-2.5 hours a day 4 times a week. How much do you think my breasts will shrink? I'm 5'4 with an average built (not bulky or fragile) 21% BMI. Help! I'd like to know how flat I can expect to be :(