How do you delete a tag set?
The documentation covering Groups and Tags is here at https://docs.civicrm.org/user/en/stable/organising-your-data/groups-and-tags/

To view tags, go to: Contacts > Manage Tags (Categories) in the navigation menu.  A tag can be edited or deleted using the respective links in its row.  If it is a reserved tag, remember to first untick the reserved box.
Hope this helps.