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If what you meant is automatically remove the original one (only the thumbnail uploaded), AFAIK, there is no default way to do that since XThreads needs it to rebuild the thumbnail if the user decides to change the thumbnail settings later and run the Rebuild Thumbnails feature.

If what you meant is you want only one thumbnail (the example is using 2 thumbnails), then just change the Image Thumbnail Generation setting, then run the Rebuild Thumbnails.