How do I delete one of my custom templates in Numbers - OS 10.10.1
Rename or delete a custom template
After you install a template, it appears in the My Templates category in the template chooser.

In the template chooser, Control-click the template name, then choose Rename or Delete.

If you’re renaming, type a new name, then press Return.

You can’t rearrange templates; they always appear in the order in which they were added.