basically you DO NOT "upgrade" major versions of programd on CentOS / RHEL
what centos 5.0 had 5.9 WILL STILL HAVE
now
you "can" replace 2.2 with 2.4
BUT and this is a VERY big BUT
you will need to build the WHOLE STACK from source
php
MySQL
PhpMyAdmin
Apache
( and anything else needed)
SEE:"install instructions"
http://httpd.apache.org/docs/2.4/install.html