Dashboard > News & eNewsletters.
Click Create eNewsletter.
Click eNewsletter Header. Here you can select an image to upload for your header. When creating your header keep it at 601 pixels wide, as this will mean that it will not distort when uploaded. Make sure you have the “Use Custom Header” box ticked, or it will not show.
Click Done when finished. This image will nos display at the top of your eNewsletter whenever you send one.
You can click Preview to see what your newsletter would look like before you send it.
eNewsletter header images should be 601 pixels wide, but may be any height (although a height of 100 - 150 pixels is recommended).