I agree with everyone that says you can't spot reduce, although you CAN do more specialized training to counteract this. It's called gynecomastia and its caused by a hormone imbalance in males. Basically, you're increased your estrogen-to-testosterone ratio in estrogen's favour.
LUCKILY for YOU, we've got solutions
You can indeed train to produce certain hormones over others, such as for growth hormone, testosterone, or IGF-1.
For your case, you would want to increase testosterone levels, which will tip the estrogen-to-testosterone scale to testosterone's favour
To do this you must train with high weights, low reps...somewhere in the 2-4 rep range.
Lets say
5 sets of 2-4 reps with 2 minute rests in between.
Try to lift something that you can only lift 2-4 reps, no more. This may take a while to experiment, and there are 1-rep max calculators, but i find they're sorta off....here's one if you'd like
http://www.exrx.net/Calculators/OneRepMax.html
You want to stimulate as many muscle fibers to elicit the highest testosterone release so follow my recommendation.
REMEMBER TO WARM UP!!! Warm-up by lifting half the weight you're gonna lift and do about 10-15 reps, rest up, do 75% of what you're gonna lift for about 10 reps then start the set.
Do 5 sets of 2-4 reps for
1)
Barbell Deadlift (you should be doing deadlifts as they will increase your fat loss and muscle mass, and if not please learn this exercise)
2)
Barbell Squats
3)
Barbell Bench Press (or with dumbbells as it's safer in my opinion)
That's all the exercises you'll need, they're huge compound exercises that will not only kick those "man boobs" out of town, but will build muscle and burn LOTS of calories because of the high intensity.
P.S. Don't forget, testosterone is fat burner and very anabolic which helps muscles grow.
Goodluck, message me if you have any questions
-Dmtiro