You've already saved a Template and you need the name changed? Editing the templates is easily done by accessing the Template Selector page, under New Broadcast. On the top right corner, you'll see a Filter: drop-down menu:
Where you need to click on the Manage user templates. A new page will open with all the templates you've created, where you'd be able to edit the name.
Another way of accessing the user template page is by putting /emailtemplate into the URL.