I couldn’t find a way to do it through the settings themselves so I edited the page code:
Under Appearance > Editor, click on “header-banner.php”
Find this:
<img src=”<?php echo of_get_option(‘default_banner_image’); ?>” alt=”<?php bloginfo( ‘name’ ); ?>-Banner”>
<?php else: ?>
<img src=”<?php echo get_template_directory_uri() . ‘/includes/images/banner.jpg’?>” alt=”<?php bloginfo( ‘name’ ); ?>-Banner”>
And replace the bits in quotes with the URL to your image (you can upload it to your media library)
So it would look like:
<img src=” your image url “>
<?php else: ?>
<img src=” your image url “>
Tested and it works!