How do I change my background on my MacBook? On my MacBook Air, I accidentally somehow pasted a picture on Olaf on my screen and when I try to change it, it just goes into a black screen. I have tried changing the screen saver and it just doesn't work. Does anyone know what's wrong with my computer?
The easiest way I've found to do this is to simply right click on the desktop, which will open up a popup menu (see screenshot below of popup menu). 

NOTE: Right clicking can either be a 2 finger click or a 2 finger tap (depending on how you have your gestures configured).



Then from here you can change the image.