Lose weight?

I'm 13 years old and I'm like 5'4 and 135 pounds [sometimes a little more] [[I've already lost 40 pounds]] and i want to lose weight-How much weight do i need to lose and what exercises could i do? I especially don't lke my thighs arms or my stomach-yeah and I have a friend who i think is trying to lose weight and shes my age and about my height and i think shes in the 170s or something like that so maybe things we could do together?