The shop header background and title can be changed with the WordPress customizer. Navigate to Appearance > Customize > Webshop Setup.
For best result the background image must be at least 1140 pixels width.
Title and subtitle
The shop header displays the page title and some text beneath. Set this text under subtitle. Change the page title of your shop page if you want tot display another title.
With the Text color you can change the color of the subtitle.