Change url of page according to my requirements in wordpress

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Are both ?page_id=5 and About.php same page? If yes:

  1. First go to Settings > Permalinks > Permalink Settings and change the Common settings to anything other than the default.
  2. Once configure use this plugin: http://wordpress.org/extend/plugins/php-to-pages/ or any other that’s similar.

Make sure the Page slug is edited according to your liking. You can edit the page slug individually from Pages > Pages.