Actualizacion de Php

He instalado Joomla 2.5.8 para un nuevo sitio y al instalar Akeeba me surgela siguiente advertencia:
You are using an outdated PHP version
You are using PHP 5.2, a version of PHP which has been end of life since January 2011. It is insecure and lacks a lot of features introduced in newer versions. Akeeba Backup is still compatible with it and will continue working just fine. We are planning on removing support for it in the following months. You are strongly advised to upgrade PHP for reasons of security and compatibility with future versions of Akeeba Backup. All Joomla! extensions written since mid-2011 and the Joomla! CMS itself are already fully compatible with PHP 5.3.

Partiendo de este mensaje pregunto lo siguiente:
[b]
Como puedo Actualizar Php de PHP 5.2 a PHP 5.3?[/b]