I have just been working on a site that needs PHP 5.2 or above. The stock repositories for Centos that are provided by Virtualmin do not contain the PHP version I needed. However they do provide a Bleeding Edge packages, these must only be used if you know what you are doing as many of the packages are not stable.
To add the Virtualmin Bleeding Edge repository run the below command while logged in as Root either into the console or via SSH;
Then to update the PHP from the Bleeding Edge repository type the following;
yum update php
Restart apache and you will then be running a newer version of PHP.