Navigate to the pages library of your department by following the View and Edit pages instructions.  

Once in the Pages library, select the ellipsis (…) on the row of the page you'd like to update, and select Edit.  The page properties drawer will appear on the right.  Enter the page name, URI, and Description (if desired) into the Name, Identifier, and Description fields.  Next, click Save Draft to save the page without making it publicly accessible or Publish to make the page publicly accessible.

Note: the page URI may only contain alphanumeric characters, underscore ( _ ), dash ( - ) and space and must be unique, unused by any other page in the pages library.  Additional languages can be selected to create locale specific pages if desired.