How do I control the layout on the WP Tag Archives template?

I’ve installed the tag cloud widget on one of my sidebars. When a user clicks on a tag, the site displays the a list of the posts associated with the tag on a page using what I assume is the WP Tag Archives template. I’d like to style that page, but can find no way of doing it short of diving into the code, which I’m not good enough to do. One example of the styling I’d like to do is that the page displays with a wide right sidebar (blank)… I have the Highend default layout option set to “full width”, but the sidebar still displays. How can I manipulate the layout of that page?