I'm 16, 5"11, 77kg.. Help?

I'm a dude. I used to be 65kg last year but I started weight lifting back then and gained 12 whole kilos of both fat and some muscle. (more fat though cuz I've been eating so much..) I wanna try losing all this belly, thigh flab over the summer (3 months.) Like.. Get a flat stomach and thinner legs. Would that be possible? I wanna maintain my muscle size too. Like I dunno if they'd.. "deflate" if I started losing weight. What workouts should I do to lose fat all over my body? What should I eat over the next 3 months? Thanks.