This is a video tutorial : https://youtu.be/3sFqWTJaviU
The first ten minutes show how to get the mesh ready for upload to Sansar as a custom avatar, and how do do some minor editing to change the shape. So If that is all you want to do, and keep the original textures, that is all you need to watch.
The next half hour or so is more specific, it probably doesn't show anything interesting to most people.
What I do is take part of the mesh to another Software, 3d-Coat, where I do some further editing to the shape and also generate new PBR textures for the skin. Nothing fancy, just showing the process, and the result. What I think is interesting, in case you wonder, is that it involves no weight painting, and no weight cleaning at all. While exporting, editing, reexporting and importing back to Blender, I am mindful of the vertex ordering of the mesh, I need to keep it intact. That is, the vertices are moved around, yes, but the mesh is basically the same, that is, it has the same number of vertices, and they come in the same order. This allows for transfer of weight by topology, which is very precise, hence, no cleaning.