Tags can be managed by a site administrator or manager (or any other user with the capability moodle/tag:manage) in Settings > Site administration > Appearance > Manage tags.
The manage tags page provides a list of tags, together with information on their creators, how many times they are used, when they were last modified and which tags have been flagged as inappropriate. Inappropriate tags are shown in red when using the default theme.
Selected tags may be have their flag reset (in other words remove the inappropriate flag) or be deleted. Tag names and types may also be changed.
The manage tags page also allows for official tags to be added. Official tags are tags which are added by a site administrator and are displayed to all users of the Moodle site when adding a blog entry. Creating a set of official tags for commonly used topics can reduce the amount of duplication in blog tags.