The default layout for the product page is 2 columns: content and right. You may want to change it, so this is how it’s done:
Locate the catalog.xml file under your theme/layout folder. If you can’t find the file, copy it from the basic package.
Scroll down to the section named:
There, on the first block that is nested within the <catalog_product_view> tag, locate the line:
Change this line to:
Refresh the page - you're done!