CentOS packages appears to only have PHP 5.3 available at the moment. But these commands seemed to works
rpm -Uvh http://mirror.webtatic.com/yum/el6/latest.rpm
yum remove php-common # Need to remove this, otherwise it conflicts
yum install php54w
php --version # Verify version has been upgraded
You can also use
php55w or php56w as required.
PHP Version Upgrade
more from http://stackoverflow.com/questions/21502656/upgrading-php-on-centos-6-5-final
http://anandarajpandey.com/2014/04/21/virtualmin-upgrate-php-5-3-to-php-5-4-php-5-5-or-higher-version-from-yum/