This is my first time tackling this so please correct me if my terminology for this wrong.
I have a div box that’s going to be 500 in height and 500 in width, in it I will have text content when it’s first loaded. At the bottom I will have a button that says “click here.” When that button is clicked I want to change the background on the box and load images.
Please refer to the drawing below:

I’d personally take a different more straight-forward approach. That is, if all you need is a few images you might as well fetch them in advance and hide them, skipping unnecessary server requests:
Working fiddle
CODE:
HTML:
CSS:
JS: