I am 5 feet 7 inches and 135 lbs. Not bad, right? I really do want to lose 5lbs and tone up my abdominals and lift my slightly flabby chest… Mayde starting with a 4pack and just rising my flabby chest would be nice. Any tips? Push ups, crunches? What can i do?

im 15 years old and living in derbyshire and i have a problem ,when i stand up i look slim and strong though when i sit down i get 3 big belly fat rolls and my flabby chest appeares how can i get rid off these and posibbly later build some muscle.i weigh 172 pounds and i am 6ft tall