Taxonomy is generally established at the PublicInput account's creation, and is usually planned and regulated by the account owner, organizational head, or your IT department. Please reach out to the head of your department or organization to determine updates that can be made to your Organization's Taxonomy structure.
In order to archive a level, all tags must first be migrated to another level or removed. The option to archive the level will then appear. In the example below, this option does not appear because the lowest level (Sub-Tags - Level 4) has tags in it.