Theme settings > General Layout
You can make your content wrapper boxed or full width
Background repeat : Specifies how to repeat the background images. both vertically and horizontally.
Bckground size: Specifies the size of the background images.
Background attachment: Specifies whether the background images are fixed or scrolls with the rest of the page.
Background position: Specifies the position of the background images.
Background image: Choose image from libraries.