How to change blog background

Our backgrounds work best if you use Blogger's 'minima' template. First you must sign into to your blog and click on 'customize' at the top of the page. Once you have done that you then need to click on the 'edit html' tab. Scroll down in your html to where you see this:
body {
background:$bgcolor;
margin:0; color:$textcolor; font:x-
small Georgia Serif; font-size/*
*/:/**/small; font-size: /**/small;
text-align: center;
Change that part of the code to say this:

body {
background:$bgcolor;background-image:url(direct link);background-position: center; background-repeat:no-repeat; background-attachment: fixed;

margin:0; color:$textcolor; font:x-small Georgia Serif; font-size/*
*/:/**/small; font-size: /**/small;
text-align: center;

Now all you need to do is choose the background that suits you and copy the link underneath it and then paste it in your html between the parenthesis where it says direct link. Preview your changes and then once you have checked that everything looks right be sure to save your template. Voila!

Source: http://simplychicblogs.blogspot.com/