Go to Appearance >> Customize >> Theme Style Settings
From here you can change the color of the theme of your choice. And you can select the layout of the theme, boxed or wide.
Wide Layout
Boxed Layout
To add the background image, Go to Appearance >> Customize >> Colors & Background >> Background Image
Skin Color
- Enable custom color skin: Enable/disable the custom color skin from here.
- Skin Color: Change the theme skin color from here.