The side columns are called sidebars in this theme.
You can turn off either of them, or both, I guess. I'm not sure why you'd choose this theme if you didn't want at least one, though.
Under Appearance/Atahualpa Theme Options/Sidebars, you can uncheck all the Displays On boxes to remove the left or right sidebar completely. You can also have either one not show up on certain categories or pages. I use both sidebars most of the time, but on one page where I want a map to be pretty large, I have the right sidebar disappear. I just put that page's ID number in the Don't Display on Pages field. Very nifty.
Flynn's a genius. :-)