Kim,
From the top menu in the admin, click Themes > [theme name], then from the left menu click Page Header.
From there, you can add an image to the Custom HTML area that is there by default, or add additional HTML snapins. There is a picture icon on the top of the HTML editor for inserting an image, much like Word.
If you need further assistance, please enter a support ticket from the Support Requests menu above and we can pull up your trial and provide an example.
Stefan Barlow
Systems Architect
AmeriCommerce