Your new Centox 6.x server running Plesk 12 will need to have PHP and MySQL upgraded before going in to production.
You can do this using the Atomicorp repositories.
Check the current PHP version
php -v
Download the Atomicorp repository and keys:
wget -q -O - http://www.atomicorp.com/installers/atomic.sh | sh
Use yum to upgrade PHP and MySQL
yum upgrade php mysql
Add the most commonly used PHP modules as required
yum install php-ioncube-loader php-mcrypt php-bcmath php-zend-guard-loader db4-utils
Restart the apache/httpd service gracefully…
service httpd graceful
…and test your PHP version.
php -v
Your PHP and MySQL upgrade is now complete.