Every WordPress.com blog and every WordPress.org install can be used as a content management system. One does not need any sort of upgrade to create a website structure.
A WordPress blog can either be structured as a page based website or its conventional post based blog structure can be retained. That’s why understanding the differences between posts and pages, comprehending the SEO implications of creating a page based structure, and knowing how to use custom menus are key to decision making when selecting a theme, and setting up your WordPress.com blog. http://onecoolsitebloggingtips.com/2010/05/12/better-blogging-at-wordpress-com-pages-and-posts/
See here for a step by step guide > Using WordPress.com to Create a Website http://en.support.wordpress.com/using-wordpress-to-create-a-website/
See also http://wpbtips.wordpress.com/2011/12/19/custom-menus/
On one hand, none of the characteristic "blog" features like categories, tags, authors, dates, etc. can be removed from a free hosted WordPress.com blog without purchasing an annually renewable custom design upgrade and doing the required CSS editing.
On that other hand, one can edit a WordPress.org theme free of charge. That's why I suggested you read this comparison > WordPress.com and WordPress.org: The Differences http://en.support.wordpress.com/com-vs-org/