How to loose belly fat without losing wieght?

i am 21, weight 73 kgs and height is 5.10 feet. i was highly under weight but now i have gained enough to be called normal. i go to the gym regularly and all of my body parts are getting toned but my problem is my belly. Its not too bad yet(in fact it protrudes out just a tiny bit ) but i want to control it before it gets worse. please give me tips on how should i loose my belly fat and build my abs without loosing the precious weight i have gained........ plus should i tone my legs during i tone my upper body or the legs can wait until i am done with what i am doing?