Backgrounds Inaccessible?

Please excuse me if this question is regarded as idiotic, but I only started using this software yesterday (and it's amazing)

I have also searched for a related topic thoroughly, and only found one to do with backgrounds staying black

My problem, is that the backgrounds are inaccessible (apart from the default), but they are not greyed out
(I want to set photo's etc. as my backgrounds)

I can customise category icons, and everything else is fine, just need to do these backgrounds to perfect my set-up

Any assistance in this area would be greatly appreciated, and I thank you in advance for taking the time to read my noob post

Hmm. I restarted my computer for other reasons, and now I can change them

Though I created a source folder for the images I wanted to use in the pictures section, before I attempted again

So I'm not 100% sure whether it just needed a reboot, or did the source folder make a difference. Not a major issue anymore, but if anyone could shed some light on this, it would be very helpful in the future.

Thanks again.