Screw Up

So i went to change my background on my blog. Instead of using the normal site i get my backgrounds from i ventured onto another site to try them out. Well it has me change some stuff in the settings and then put in the html code. When i realized it wasn't working like it should have i tried to get it back to normal and failed.

I can not for the life of me figure out how to get it back to minima (or what ever it is called) so that i can put a background back on it. So for the time being i guess i am stuck with hidious (well not that bad) programmed background.

Can someone help me out please. How do i get it back on Minima or Picture Window Templates? This is the first time i have had to mess with any of this since they changed the stuff around. Boo hiss lol! Maybe i should just do a blog makeover and have it done by professionals and personalized.