With cPanel you are not really managing a CentOS server as such, you are managing a cPanel server running on a basic CentOS base. It installs and manages its own Apache, PHP and MySQL builds.
The cPanel interface for the root user has the facility to upgrade or downgrade Apache and PHP between the officially supported versions. First make sure that cPanel itself is fully up-to-date (most install update automatically, but it is worth checking) then check to see if the version you want is already in the lists so you can upgrade to them that way.
You can install your own Apache/PHP/what-ever, if none of those in the standard cPanel build are not recent enough for you, but it is not recommended as you will lose any official support you might have from the makers of cPanel and your custom setup migth get broken next time there is a significant update to cPanel.
edit: I forgot to add: the management interface referred to above is web based, usually find it at
http://<server>:2086. It is a while since I've used cPanel as either as user or an admin but back when I did the official forum and parts of webhostingtalk.com contained many useful discussions.