The header background image field controls the banner at the top of your website pages. The ptEnhance themes have a default image in this spot, see the images below.
Step 1: This can be replaced by uploading your own image into the header background image field on your Website then go to Colors and Settings page. The size of this image is 960 pixels wide. The default images are 350 pixels high, but your custom image can be between 150 and 350 pixels high.
Note: For best results you should size your image to fit these dimensions before uploading it. You will want to find or take an image that is more rectangular than square, wider than it is high.