To completely remove the skin box from pages which user sees after they login

  1. Browser to the template folder on your server
    Templates files can be found at /Templates/[Skin Name]/Default.html
    Default.html is Template file
    [Skin Name] is name of the skin you want to edit
  2. Open the Default.html page and remove the TAG [+BUILD_SKIN+]
  3. This will remove the Skins Box Completely from User pages

If you have also removed the skin box from login page then default skin selected in admin will automatically load for all users