The CentOS 5 EZ template released by the Russian mafia at Parallels contains an old version of PHP and is yum-less. The first step to upgrade this is to install yum with this huge number of packages (thanks Sohail).

Next install the great atomicrocketturtle repositories:

wget -q -O - http://www.atomicorp.com/installers/atomic |sh

And then finally update PHP:

yum upgrade php

If upgrading from PHP 4, there maybe some additional config files to mess with. See atomicturtle’s wiki page on PHP for troubleshooting.