add_action('init','change_author_permalinks');
 function change_author_permalinks()
 {
      global $wp_rewrite;
      $wp_rewrite->author_base = 'member'; // Change 'member' to be the base URL you wish to use
      $wp_rewrite->author_structure = '/' . $wp_rewrite->author_base. '/%author%';
 }