First off, you really need to severely optimize your background image. Right now it is 4.6MB and anyone on a slower internet connection will not wait for it to load, they will likely just go elsewhere. Not to mention that the search engines take into account total page size and loading times when calculating search engine ranking and placement which means your site might take a big hit and end up far lower in search results.
Background images should never be over 100k in size and at an absolute maximum, 250k.
This will do it, but you won’t be able to read anything till you change all the text colors, and you are unlikely to find any text colors that will work with all areas of your background image. Good luck with that.