@editorg1 – the theme uses Bootstrap 2 and therefore the elements spanX are employed as wrappers for various elements. So the process of reducing the sidebar or any other elements is a bit involved than just adding some css rules here and there.
What @arty9k suggested will work but will leave you with a chunk of white space to the right of the sidebar – adjustments will need to be made else where to compensate the change.
Best starting point is a child theme to which you’ll then need to add the files home.php, page.php and single.php all copied over from the parent theme.
In all of the files above you’d then change the <div class="row" role="main"> to <div class="main row" role="main"> and the <div class="span8"> to <div class="content span8">. You can now target these new elements like so (adjusting the values to suit your needs):