From the LiveWhale interface, click the "Pages" tab. (If the Pages tab does not appear, the administrator has not assigned page editing permissions to you.)
If the page you're looking for is in a navigation, click its title to view the page details screen. Otherwise, click the "File Browser" submenu, navigate to the page's directory, and then click the name of the page.
On the page details screen, click the link "Delete this page". The page will be deleted.
If you wish to restore a deleted page at a later date, see "Restoring a deleted page".