I realise this should probably be in Forum Guides, but I'll write guides on all the new features soon. This is self-explanatory really. I've added lots of new backgrounds, though I realise I need to give some characters more backgrounds. I just chose the ones I've already taken screenshots of for the time being. Feel free to suggest parts in the anime that you think would make a good background. Not every background is perfect for this theme, because obviously it has to be darkened for readability. Here's how to change yours:

Set New Backgrounds!-bgupdate-jpg

That will take you to your profile options. You'll find the setting to change your background at the bottom. Have fun.