Reset options when customizing theme

When customizing background colors and image I do not see how to remove the customized setting. For example, I set a custom background and then go back and the background doesn’t show up in the customization screen as though there were never any customization. It does not allow me to remove the previous background image, only replace it. I would like to set the background with custom settings, no repeat etc and I can do that in the css file but the customized settings are overriding that. Can you help me remove the custom settings? Thanks.