https://hellagoodsims.tumblr.com/post/173001039053/learning-how-to-convert-a-high-poly-mesh-to-a-low
Retopology 101
This is a tutorial that shows how to turn a mesh with a high polygon count into a simplified mesh with a smaller amount polygons by using a simple shape and the shrinkwrap modifier.This is most helpful to those who use programs like Marvelous Designer to make their cc because sometimes the decimate modifier isn’t enough for cutting down the polygons. With this simple technique, you’ll be able to maintain the shape; keep the essential details of mesh and most importantly, helps makes the size of the file more manageable. Your game will thank you.