Navigate over to the products page and view the table of products.
Find the product you wish to delete manuals for, and hit the green 'Manage' button at end of the desired product row.
This will load you into a 'Manuals' page. From here you can hit the red 'Delete' button at the end of each manual file row. A popup confirmation will be presented before any deleting is actioned.
Please note, the deleting of a manual file is irreversible and we wont have a backup copy so be careful