Surgery. You are referring to gynecomastia. Breast tissue beneath the nipples enlarges causing nipple protrusion. Surgery involves an incision along the lower 1/2 border of the pimented areola surrounding the nipple and excision of the enlarged glandular tissue with electrocautery.
Male breast buds. For adults, the only available method is surgery, unless you can identify a medication that is causing it (eg., spironolactone, cimetidine, etc.), prostate drugs like flutamide/finasteride, or certain HIV medications.