You can permanently delete an unused template from the list. You can also make a rarely used template inactive and hide it so it doesn't show in the Templates list.
What’s the difference between a deleted template and an inactive template?
Make a template inactive when you rarely use it but want to keep it available for use at some time in the future. Also make the template inactive when you'd like to delete it but can't because it was used in a transaction. All transactional information remains associated with the template, even after it's been made inactive. After making the template inactive, you can hide it in the Templates list. You can view inactive templates and show them on the list again at any time.
Delete a template only when it has never been used in any transaction. Deleting a template permanently removes it from the Templates list and from any drop-down lists that use templates.
To do this task
Go to the Lists menu and click Templates.
Select the template you want to delete.
Click the Templates button at the bottom of the list and then click Delete Template.
Click OK at the prompt to delete.
Hide a template in the Templates list