To remove the Articulate mention in the email, search for:
<emailfooter>Powered by Articulate(tm) - https://articulate.com</emailfooter>
... of the XML file for each template you would like to change:
You should only modify xml files using Notepad.
Please note this article discusses modifying files in your Program Files folder and is not supported by Articulate. Articulate is not responsible for any issues that would arise from following these steps.