How do you customize this thing??

Man! So I’m trying so hard to figure this whole thing out and then I was looking at everyone’s blogs and noticing that they are so cute and not the custom templates that the blog gives you at first ... they are all cute and different! so I went on one of my friends blogs and it had a web site on the side of where to go to get your own custom blog background ( http://thecutestblogontheblock.com/ ) ... so I found one I think I like but I figured I would just try it to see if it would work ... it didn’t ... :( obviously!! Because if you look closely you can see at the top left corner some red ... well it’s suppose to be a Beautiful Butterfly! ... But its not getting rid of the old background now ... and I have no idea how to do it!! :( And the thing said it would be easy...? Maybe I’m just not good at this stuff?? ... So anyway, if any of you could help me figure out how to customize my blog I would really be thankful!! I like the old one but I want something that’s really me ... so ... ??? Anyone?? ... Please! :)