What content you want to change be specific ,  if you want to remove the powered by elgg follow the below link

https://community.elgg.org/discussion/view/44250/how-to-change-or-delete-powered-by-elgg?offset=10

@yassine

views\default\page\elements\footer.php

views\default\page\elements\foot.php

that what i found in footer.php :

<?php
/**
 * Elgg footer
 * The standard HTML footer that displays across the site
 *
 * @package Elgg
 * @subpackage Core
 *
 */

echo elgg_view_menu('footer', array('sort_by' => 'priority', 'class' => 'elgg-menu-hz'));

So what i can do to remove powred by elgg and add some titles ...