This depends on your distributions specific repositories, in your case CentOS. If it isn't available, you might volunteer to provide such a package to the repository.
On Fedora systems the main repositories provide PHP version 5.2.6 is the current state. I'm not sure if you can use Fedora RPM's on CentOS. Even if it installs properly, you might want to remove the previous PHP installation to avoid any confusion due to different install locations of the RPM packages (if there are any differences for PHP).
Alternatively you could build from sources, but that would mean that you have to update each new version by building it yourself to stay on bleeding edge of development.