My brain isn't working anymore (surprise)and I want to put a new one in. I know how to change the one I have now to an older one but I want to put in a new one.
Generally you will find a setting for screen saver (as opposed to background). In most cases you simply choose the one you like or add a new image.
Just do a search on changing the screen saver for your particular operating system.
I just typed Screen Saver into the little search window
at the bottom and got lots of choices, Sassycakes, see
the picture below, you will see your own picture through
the one that I have posted.