To completely delete one or more tags, you need to:

Step 1: Navigate to the 'Manage Tags' section under the Event Settings

In your event's left navigation menu locate Setup and select Event Settings. Under the Event Settings, at the bottom of the screen locate the Manage Tags section and click on it.

Step 2: Locate the tags you want to delete and click on the trash can icon next to them

The tags management section allows you to see and delete the tags you've added to your invitees. To delete them, click on the trashcan icon next to them and confirm your intent. After doing this, the tags will be deleted.

Note that all invitees and guests tagged with the deleted tag will be untagged and this tag will no longer be available. If you've set a form question to be asked to only invitees tagged with that tag, the question will be asked to ALL invitees.