Why can't i get my custom background OFF my tumblr?

I am having some trouble with my custom html on tumblr. About a month ago, I added a custom background to my tumblr (micheleface.tumblr.com)...its the pink and green heart background that is currently on my page. I’ve read just about every tutorial available and edited my code, entering a new background url and everything…but the old one will not go away, no matter what theme i use or how i edit my custom CSS. I’m usually pretty good with this type of thing, for some reason the url for my old background is somewhere that isn’t accessible to me and it is really frustrating. I’ve cleared the temporary files on my computer and cleared my cache and stuff, so i know it isnt just because a cached version of my tumblr is showing. I have a feeling its because recently the customization interface for tumblr was changed a bit, and i added my current background before this change was made. I’m about to rip my hair out!! can anyone help?