This feature is available in Enterprise and Ultimate editions.
Follow these instructions to learn how to delete a story/backlog item or defect template.
When you delete a template, all associated details, tasks, and tests will also be deleted.
Go to Product Planning > Templates.
Select the template you want to delete, and then select Delete from the Generate Story drop-down list.
In the pop-up window, click Delete. The template will be permanently removed from the system.
You can delete multiple templates simultaneously. Select the checkboxes to the left of templates to be included in the deletion and choose Delete from the Move to Project drop-down list, then click Delete on the Delete Items page.