The commands below outline how to install PHP 5.5 on a fresh CentOS 6.4 installation using the Webtatic EL yum repository.

First, you'll need to add the Webtatic EL yum repository

$ rpm -Uvh http://mirror.webtatic.com/yum/el6/latest.rpm

Now, you should be able to install php55w and php55w-opcache using yum

$ yum install php55w php55w-opcache

Now restart apache

$ service httpd restart