In Magento Admin section you can change the layout of the “products” page  (from the “manage categories” menu) but there is no option to change the  layout  of  the  “product” page.

You can only do that by hand, and you must edit the “catalog.xml” file here: app > design > frontend > default > deault > layout > catalog.xml

Do a search for “Product view” and look for page/2columns-right.phtml some lines below. You can change that to one of the available layouts