I deleted the header image and upload a new one. The image selected was too small and undesireable for the header. I deleted image and tried to upload a new one, unfortunately, the new image was not recognized. (although, the 2nd image was within header guidelines).
When I deleted the 2nd image, nd saved, I returned to portfolio page, only to see the deleted image in the header.
To clarify, I replaced the sunset header with a new image of a local mountain, which was too grainy. When I deleted that mt image, and saved, there was no header image. However, when I tried to upload a replacement image, it would not upload. When I 'saved' and returned to upload settings, the old picture returned.