Hi:
 
I know how to change the logo, but how do you change the background where the logo sits? Which file get altered?
 
Thanks

Change the logo through the System/Global Settings/Logo Settings. The backround is done through the stylesheet for your theme. You can find the stylesheets annotated http://www.viart.com/css_reference_table.html

Can you help as to where I need to alter the Header background (Where the logo sits) please?

it's via css - search the forum for css and you'll find the style sheet (very limited) for the position of the logo