How to redirect old url alias to new url alias?
You can use redirect module to redirect url from "old url" to "new url".


  This module allows you to specify a redirect from one path to another
  path or an external URL


There is also global redirect module which provide the same functionality.


  
  Checks the current URL for an alias and does a 301 redirect to it if    it is not being used.
  Checks the current URL for a trailing slash, removes it if present    and repeats check 1 with the new request.
  Checks if the current URL is the same as the site_frontpage and    redirects to the frontpage if there is a match.
  Checks if the Clean URLs feature is enabled and then checks the    current URL is being accessed using the clean method rather than the
  'unclean' method.
  Checks access to the URL. If the user does not have access to the    path, then no redirects are done. This helps avoid exposing private
  aliased node's.
  Make sure the case of the URL being accessed is the same as the one    set by the author/administrator. For example, if you set the alias
  "articles/cake-making" to node/123, then the user can access the
  alias with any combination of case.
  Most of the above options are configurable in the settings page. In    Drupal 5 you can access this after enabling the globalredirect_admin
  module. In Drupal 6, the settings page is bundled into the module