Making Background Image Bigger

I am trying to take an image that I have in the background and make it larger so that I can get the part of the picture I want to see around my sidebars and body of my website. The part I want is hidden behind and I just want to make the image bigger within the background so that the part I want shows. I have been messing with CSS code to try to do this without success.

My website is: https://grangerwashington.org/