Go to "Tasks", select "Templates" from the left-hand menu and select the template you wish to archive. Then click on the "Status" drop-down and change from "Active" to "Deactivated".

You will then receive a message asking if you would like to delete all future tasks created by this template or keep the current tasks but not create any new ones. Click "Apply Changes" and then "Save Changes" in the template.

The templates are deactivated, so you can reactivate it at any time.