Breast tissue is 90% fat. That is one of the reasons womens body fat % is higher. If you want to lose breast tissue, which remember is 90% fat, you have to lose fat. However there is a trade off. The body does not spot reduce fat. In other words you can not tell your body to lose fat in the breast and no where else. So when you start a program to lose fat, it loses it every where in equal proportions. I'll be honest with you sometimes, you just can't lose the weight from your breast. Here are some things that might help you out, I do know that sometimes losing weight does reduce the size of your breast. There are certain work outs that you can do to achieve some goal of losing some "fat" tissue from your breast. There actually is a work out that involve your breast, I'm not sure if you knew or if you tried them but if you didn't then try them out and see if it works. You can put your arms like a genie and move your breast muscles, and what that is going to do is basically firm them, and when you firm you tend to get small, maybe of course not dramatically but you will notice it. It might feel a little silly to do that work out, but hey! there isn't a work out that sometimes doesn't look funny lol.
Go to a gym or physical therapist and get your body fat tested. This is something that most gyms do for free. If you are greater than 25% than you could stand to lose some fat. However, if you are less than 20%, you are normal and I would not recommend losing fat.
Eat 6 small meals per day, about 300-400 calories per meal. Balance the grams of protein and carbs with each meal as much as possible and eat lots of vegetables.
Use intense cardiovascular exercise to elevate the metabolism and thus burn fat. 4 times a week, do a maximum of 20 minutes of vigorous cardio. Run, bike, whatever, but do it hard all the way to the finish. Feed your body good nutrition like I recommended above, then let you metabolism burn fat. Only do this if you have greater than 25% body fat though.
Follow this recipe as best you can and you should lose fat. It is hard to say how much your breast size will go down, but doing this will no doubt make you healthier.
Well I hope this works out for you and I hope you go to the size that your aiming for!