You can delete only manually assigned tags.
To delete a manually assigned device tag:
The list of tags is displayed.
The device tag is deleted. The deleted tag is automatically removed from all of the devices to which it was assigned.
When you delete a tag assigned to the device by an auto-tagging rule, the rule is not deleted, and the tag will be assigned to a new device when the device first meets the rule conditions. If you delete an auto-tagging rule, the tag specified in the rule conditions will be removed from all devices to which it was assigned but will not be deleted from the list of tags. If necessary, you can manually delete the tag from the list.
The deleted tag is not removed automatically from the device if this tag is assigned to the device by an application or Network Agent. To remove the tag from your device, use the klscflag utility.