Set Thumbnail 

  1. Click and hold on the thumbnail of the file that you want to use as a thumbnail (image Files Only; jpg, png, gif)
     
  2. When you move the mouse a thumbnail image of the file will display beside the mouse cursor

  3. Position the mouse cursor over the thumbnail of the file that you want to customize

  4. Release the mouse button

Reset Thumbnail

  1. Click on  for the file that you would like to reset, then click Reset Thumbnail