I am a bodybuilder and I have 5 years bodybuilding. To make big muscle small, u need to shape out your muscle which use light weights to do high reps. The good way to make your legs muscle smaller is play basketball. I talk for my own experience, I played football in primary school and my legs muscle is huge, but once I went to secondary school I switch from football to basketball. Now my legs are as skinny as my front arms.