There are two main edits you can do to the header: upload an image or logo and edit body text
To upload a logo or image click on the Content token
From there you can either select an existing library image or upload a new image. Mobile Image should be no wider than 300px in width.
You can also select the Image location. Above or Below the body text.
To edit the header Body content (text) click on the Body Token
This will give you a simple HTML markup tool to add your text. The size of the header text is preset but you can override that using custom HTML code by click the source button and pasting in your own html.