Affects ONLY Thumbnail Grid view and Thumbs+Details (not for icons, those are in MainFolderIcon folders and selectable in Settings>Theme)

- Replace these in user's folder (About>Settings folder) and 
NOT in C:\Program Files\OneCommander)

- Files are PNGs with transparent background
- Resolution 256x256

FolderThumbDefault.png is thumbnail if there are no thumbnails within
FolderThumbDefaultInside.png is thumbnail on top of which 1/2/4 thumbnails will be rendered (coordinates of those can't be changed, so use these as templates)

- This only works when "Use local thumbnails" is enabled in Settings>Preview
- Make backup of your new files you don't lose them in case of reinstall

Restart program from system tray to reload these after updating
THEN clear thumbnails database from Settings>Preview