This may sound silly but there will be conflicts/issues with the default Centos repository so you have to use a third party like remi (I prefer not to do this but it's the only option unless you migrate your sites/data to another server or can stand some downtime-not an option IMHOon a production server).
You may need to upgrade to PHP5.3 to run Joomla or many other reasons.
Your host needs to use PHP 5.2.4 or higher to run this version of Jo........