I need help lossing weight?

Hi im 14 about to turn 15 i weigh 148 lbs at the moment i really want to get down to what im supposed to... I joined my highschool swim team so i think that will somewat help me wen i get back to skool but for know what can i do to loose that extra weight? Im a very picky eater but i will eat some vegtables and fish and meat i dnt really eat fast foods cuz i dnt really like thm like mcdonalds ect. I sometimes do crave pizza but i dnt really eat/ crave it often i usually dnt eat many fruits but sometime i will go and snack on an apple or something umm junkfood i dnt really eat cuz we hardly have Any at my house so yea umm idk wat can i do to loose the weight i need to loose??? I am 5"2... Also i was fatter wen i was smaller so i have strech marks from where i lost some weight as i gre is there anyway i can get rid or make them less noticible??? Oh and how can i prevent anymore?? Ok thats it thanks :)