Upgrade PHP to 5.2.x from Plesk default PHP 5.1.x

By default Plesk installation, the PHP version is 5.1.x, if you want to upgrade it to 5.2 or even 5.3, please follow these steps:

Login via SSH as root user first.

Upgrading PHP:

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

And then follow on-screen steps.