Thanks for the links, but I can't browse the pictures on my computer or drag a picture to the menu, so I was wondering if there was some other method of changing the picture.
I tried this:
1. Went to System Preferences.
2. Clicked on "Users & Groups."
3. Hovered over the picture and clicked on the arrow.
Then, I can only use default, recents, or camera. I can't choose from my pictures.