How I can change the margin of the sides and the space below?

Hi;

I had done a web page; but the proble, is the margin of the sides and the space below;

here you can see which is the problem > http://www.willarg.com/

I  don't know, how I can remove the white spacing and down the sides so that the background image fills reaches the horizontal part of the browser without leaving those blanks

Thanks !!!

Alexander