The 3D model I bought comes with a UV and texture. But its UV layout is bad so I used the UV Layout sop to rearrange it. But how can I generate the new texture with the new uv layout?

you can bake new textures from old ones using one of the baking tools, Labs Maps Baker SOP, Labs Simple Baker SOP or Bake Texture ROP

I can't manage to do the transfer on my low poly model with high res texture to a new texture with new uv layout. If I use attribute from map sop, it will become vertex color and it looks bad.