You can update the Subject and From Name at the top. 

Select the elements on the right side and drag and drop them into the email template to customize the blocks.

Click into the text to edit the content. 

Once your email template is customized to your liking, just click "Save and start using".

To continue using the default template until you're done editing, just toggle on "Use default email".

If you ever want to revert to the original template, click "Reset to default". 

Customized Emails