How do I delete should I do about the unsued files?
Robohelp 'help' on the unused file report help' is an outrageously bad joke:
You cannot remove these files from within your project. Use Windows Explorer to delete the files.
Note: Avoid using Windows Explorer or your version-control application to remove files.
The files are not shown in project manager because they are not part of the project. They are still within the project's folders though.
If you are not using version control, then you do just delete them using Windows Explorer.
I believe the incorrect information has been corrected in later versions of RH.
See www.grainge.org for RoboHelp and Authoring tips