How to use custom backgrounds on ubuntu 17.10

Hi about a week ago I upgraded my ubuntu from 17.04 to 17.10 and one issue im having is being able to use any picture and set its size as the background. The pictures I want to use is either to small to big and I can’t find a way to have it fit like I could in 17.04. I been reading on alot of ubuntu websites and none of them are helping me with my issue or talking about the issue. Any help would be great.

I’ve moved this to the Support & Help Requests category because this site isn’t designed to take tech support questions. Sorry. I’d recommend using one of the official support channels listed on the Finding Help page.