There's a line in the "functions.php" file you'll need to change.

On or around line #53 you'll see the following line:

$mkt_options['mkt_body_content_width'] = $mkt_options['mkt_TOTAL_PAGE_WIDTH']-270-65; // Total width minus left column width, minus content padding

You'll modify the width in this line to be something like this:

$mkt_options['mkt_body_content_width'] = $mkt_options['mkt_TOTAL_PAGE_WIDTH']-0-30; // Total width minus left column width, minus content padding

and save.

And then, remove the "background-image:url(page-bg.jpg);" reference in your stylesheet file under the "#main" element on or around line #32.