You really can't do anything. Your body is set to the size you are going to be. Your still young so you may fill out more later, but your muscles and such can only get so big based on genetics. Some people are made to be bigger and some are not.
yyyyyyyy would you want thick legs I have em its not always the funnest because some guys LOVE em and some guys HATE em it gets annoying...kinda like girls with big boobs I guess they don't like em but I want em because I don't have em