Theme Skirmish

Before making any changes, you’ll need to create a Child Theme — so that your changes are not lost when the theme is updated. Then you’d need to add new styles to the new style.css file — adjusting the margin and width of these:

#content {
    margin: 0 22% 0 0;
}

#main #secondary {
    margin: 0 0 0 -20%;
    width: 18%;
}

The best way to work with CSS is by using Firebug — which enables you to see exactly what CSS code is affecting certain areas/elements on a page.