Board Thread:Support Requests - Getting Technical/@comment-5170103-20150917095424

I'm head admin on the R5 Rocks Wiki. I really want to change the wiki background to a particular image. But I can't, because the file is too big. What doesn't make much sense to me is that on some wikis, the background image is huge (for example, the Little Mix Wiki). How does that work? Is it something with the css?

I wish to use this image for the background 