Height/weight for Jv runningback?? plaese help!?

the seasons almost comming again. last year i started WR and kickoff return for freshman football but i think im a little too small this year and i think its a little boring. this year im playing JV football, the teams mostly made up of incomming sophmore with few, few, few juniors. I really want to play halfback. I am nearly positive i will be the fastest one on the team, and i could juke and get in holes easily. But one problem is i am very small , like around 5'4-5'4.5 115 pounds. so is there any way i could grow bigger is my first question. and also what should i work on during preseason. oh and also what is the average height weight for jv runningbacks.