Once you've selected a template to edit, you can click on the 'Edit Email' button.
There are two ways to edit the template:
Using the HTML editor
Simply adding additional text to the body of the email.
In this view, you can also edit the subject line.
Highlight text to expose text formatting tools:
Click on 'Save Template' when you have finished making changes. Once you have saved that template, all changes will begin sending on any new transactions.