Well, I assume you are a man since your problem is "manboobs". But this is the womens health section so you may not get a lot of responses.
There is no way to just remove fat from the chest. Only your body decides where it takes its fat from, you cannot control that. A good diet should be #1 for fat loss. Followed by exercise.
Be more specific.
Do you currently excercise? How is your diet now? whats your height, weight, and Body fat %?