I am new to wordpress, and have chosen the Graphene theme for my first site. I created a custom header, uploaded it to the media library, and then chose it as the header from the Appearance > Header page. All good so far.
But then I wanted to try a different graphic. I uploaded that to the media library, but when I go to the Appearance > Header page, I can't select it. I get a window that appears to give me a choice of the two images I have uploaded, but there is no way to select either of them.
What might I be doing wrong, please?