Hi everyone, I thought I'd give steps on how to make them your background! Sorry I'm doing it for Windows 8 because that's what I use, but I think Windows 7 would be similar. Here we go!
Minimise everything
You should see your background, right click on your background and click personalize
Click on a background you don't like/use and click 'Desktop background' (on the bottom).
You should see some pictures with ticks on them, click clear all.