Reset design files is an option and solution to update the new design image file or when an importation error occurs.  It will remove and regenerate the new files using the original files.

The button 'Reset design files' you can find at the bottom in the 'Edit Design Info' dialog which is accessible from the 'Edit'  button at the footer bar.

INFO: This option is available in server versions only.

Related articles:

Delete Designs and Colorways