You can delete a template by removing it from the inventory or deleting the template from the disk. If you remove the template from the inventory, it remains on the disk and can be reregistered with vCenter Server to restore it to the inventory.
Remove Templates from the Inventory If a template has become outdated and you no longer use it in your environment, you can remove it from the inventory. Removing a template unregisters it from the vCenter Server inventory, but it is not removed from the datastore. The template remains at the same storage location, and you can use the datastore browser to re-registered the template at a later time. You can later decide to update the template rather than create one.
Delete a Template from the Disk If you no longer need a template or need to free up disk space, you can remove it from the disk. Templates that you delete are permanently removed from the system.
Reregister Templates Templates can become unregistered from vCenter Server if they are removed from the inventory or if the hosts with which they are associated are removed from vCenter Server and then readded.