Website development

I am using a WP theme, which I am having a couple of problems with the final details. I need: to upload background images (it won't let me, even though it is supposed to); Make the accordion slider open by default with a whole picture, rather than the slices it displays when the page is loaded at the moment. That's it. I know these are small things, hence the low budget - I just don't know how to do this myself.