To delete an Email Template, select the template in Email Settings and click the Delete this Email Template button.
However, there are two situations when the Delete button will not be shown:
If the Email Template is still being used in any appointment type or reminder, TimeZest won't allow you to delete it. Update the appointment type(s) or reminder(s) to use another email template, and then you will be able to delete the original email template.
TimeZest doesn't permit built-in templates ("Default Confirmation Template" etc) to be deleted.