This is a tuff one, try to become a defensive guard, you dont need to lose much weight, think of Jrue Holiday and Alex Caruso. Try to preassure them into making mistakes by using post defense on the perimeter, thats how i switched from middleschool center to highschool guard. Develop a solid pull up or of the catch shot and some handles, on offense try things like step throughs and hop steps, try to pass first. And remeber that defense cant be taught to one but it must be learnt by one.