Lose weight around breast area?

I'd love to go down a bra size as my breast size is too big for my frame, and I've gotten ugly stretch marks on them too. I can't buy my bras at any normal teenager store, and all my bras are really expensive.

My goal is to go down 17.6lbs before the summer by training and eating healthier. 

 I'm wondering if theres any training techniques or anything at all that can make the chest area smaller? Any help is very appreciated. 

I've heard that working your pectoral muscles helps only a little to reduce the size of your breasts, but i'm a little skeptical of this. You can't focus your weight loss to just one part of your body.  I carry a lot of weight around my middle, and i can do as many sit-ups as possible, but i will lose weight on my back or on my arms.  You will probably notice a difference in your breast size if you do lose 18 lbs, but it may not be as drastic as you were hoping.  

It varies from person to person, but your breasts will shrink with weight loss, and also if you lift weights/exercise vigorously. I went down a cup size when I lost fifteen pounds and started lifting weights.

i lost 75 pounds and went down two sizes..i also did regular weight training with a focus on biceps, lats, deltoids and pecs so maybe that helped a bit? ive noticed that the loss in fat where my armpit meets my thorax has made a big difference in my cup size as well..im not so big on the top of my boobs, i don't "fill out" i guess is what it would be..yes..i think it wouldn't hurt to increase workouts on that area..if nothing else a little toning never hurt anyone, right?

I wish there was a way to alter chest size...lol. Unfortunately, breast size is genetic, so even if you're skinny, your breasts will likely always be big for your frame.