Desktop lost after update

I apologize for not being clear! I have this crazy purple thing and would like to return to the basic apple photos.

I can bring up the system preferences and see what I want but there seems to be no way to actually get them to apply to either screen.

I have restarted, tried different photo selections and walked away several times! I believe in the past just selecting a standard photo would apply it to the screen but it is not working now.

So I was able to get another graphic to apply - just none of the dynamic photos or illustrations will apply.

At least I got rid of that god-awful purple thing! Thank you!