First, click on Appearance, on the left hand side of the page

Appearance

On the menu that pops down, click on Background

Background

To remove your current background and leave a blank, white space, click on Remove Background Image

 

RemoveBG

When you upload an image to use as the background, you can either upload it from your computer by clicking on Choose File, or use a photo you already have on the website by clicking Choose Image

SelectBGImage