HELP I WANT TO LOSE MY BELLY FAT/ WEIGHT AND ALSO FAT AROUND THE BODY.?

ok, i weigh about 40-50 kgs and i am turning 12 in march 2010, i have a huge slice of belly fat around my stomach, my mum says its like really big and i should lose it and even i want to lose it but i cant.... help.... 10 points for best answer, thanks