READ !!!!!!!!!! I really need you guy's help , i need to lose weight , read !!!!!!!!!?

hey , i am twelve now , for as long as i can remember i have been , well , fat , i see my friends and they look good in anything , and it really annoys me , i am going into secondary school on the first of september i think , and i want a fresh start , i amen't asking to be a pencil , but i want to be in some category of skinny , as in i dont care if i am not a size eight (Ireland sizes) , but i want to be able to wear a dress that are in the shops on special occasion or not have to look at plus sizes on the forever 21 website , my sisters 21st is may , and i want to wear something nice , and be healthier , i dont want to die early because of my weight , i was with my friends in dundrum , they were trying on clothes and coming out and showing us and i couldnt , how can i lose weight ?????????