page width

in this section in style.css:
@media screen and (min-width: 768px)

look for:

.site {
		margin: 0 auto;
		max-width: 1040px;
		overflow: hidden;
	}

and change the width probably to 1140px so that the ad fits into the column.
be aware that your theme is responsive, i.e. changes with the browser width, so the suggested solution will only work in wide browser screens.

for a more detailed reply, post in the theme’s section
http://wordpress.org/support/theme/iconic-one