I'm running 16.04 (2020-06-18) on a Nexus 7 Wi-Fi. I'd like to change the background image.
I downloaded an image and put in into Gallery. I couldn't find a way from there to share it or move it to the background image.
I went to Systems Settings > Background. The top section says "Ubuntu Art" and has 16 images. Below that is "Custom" and a downward-pointing arrow. Flipping the arrow does nothing.
I'm assuming that this screen is where I change the image. What am I supposed to do from here? If I have to get my downloaded image onto this page, how do I do that?
(BTW, the image is a PNG, if that matters.)