You could get plastic surgery...... But then again who doesn't like huge breasts, small breasts is usually a turnoff for most men...
You can reduce your breast size by working your upper body. If you notice most gymnists have very small breasts due to them working out their pecs and upper body. That does not mean you have to become totally muscular but by working out that area of your body, it will reduce the size of your breasts by burning and turning the tissue into muscle and help keep it down.
Breast size is genetic. And those poor gymnasts don't get to eat like they should and work out constantly. Since breast tissue is mostly fat (80-90%) you have three options. One is surgery. Two, start working out. And three, learn to love yourself. I know where you are coming from on this one, and I chose the third route. Also, to help you try bravissimo.
You can get breast-reduction surgery. In the meantime, stop wearing skin tight tees.