Hello James,
Thanks for submitting a question about the Visual Editor. If you could just clarify, are you trying to change the background picture on the page itself, or change the background in the Call to Action? In the case of the Linx theme, it should be the same image.
If the former, then you should be able to change the background picture using the Customizer. Click Customize from the admin menu and choose Background.
Best,
Christopher M.