CentOS ships with php 5.1 by default, at the time of this entry (January 2012). The php 5.3 packages are available in the base repos, but the older version needs to be removed first to avoid any installation conflicts.
This entry does not involve any migration and assumes a new server is being deployed.
0. Login as root
1. Verify current version of php
2. Remove previously installed php and modules (if applicable)
yum erase php*
3. Install php 5.3 and modules
yum install php53*
4. Verify correct version of php is installed