To delete a Story Template, go to the Manage Story Templates menu.
You can get there by opening the Create Story from Template menu (found by hovering over the right-pointing arrow in the Create Story dropdown menu) and then click on the Manage Templates button. Or you can get there by going to Settings > Workspace Features > Story Templates.
Once there, click on the ellipsis next to the Template’s name and then select Delete Template.
You’ll be asked to confirm that you want to delete the Template; if so, click OK. The Story Template will be immediately removed from the list of available Templates.
Note: Once a Template is deleted, it can’t be restored, so be sure before you click OK.