How to get a six pack?

iwant to get a six pack, im 15, 6 ft 3, and weigh 80 kg ( 12 and a half stone) . im quite fit, got level 13 in the bleep test at school, i have a bit of flab, but you can still see a outlie of a 4 pack. i do situps everyday , around 50-100., and i also eat quite healthily but have chips quite often. any advice?