Related Questions:
How to change the title of an existing Document Template
Reword a Template
Change the title of an existing Email Template
Change the name of a Template
If I clone a template, can I rename it?
Procedure:
Document Templates
Click Settings from the left-hand menu
Click Templates & Files
Select Your Document Templates
Find the template you wish to edit and click on the Template title or Edit button
Click on the Template title at the top of the Template edit screen
Change the name as desired
Press Enter to Save
Email Templates
Click Settings from the left-hand menu
Click Templates & Files
Select Email Templates
Find the template you wish to edit and click on the Edit button (pencil)
In Title box, change the name as desired
Press Save at the bottom of the page