Try doing yum install php53 on a RHEL 5.6/CentOS 5.6 system, and see the following:
--> Finished Dependency Resolution
php53-common-5.3.3-1.el5_6.1.x86_64 from updates has depsolving problems
--> php53-common conflicts with php-common
Error: php53-common conflicts with php-common
You could try using --skip-broken to work around the problem
You could try running: package-cleanup --problems
package-cleanup --dupes
rpm -Va --nofiles --nodigest
Not pleasant right? Seems the only workaround is to issue a yum remove php php-cli php-common, watch the dependencies and reinstall everything. The only thing that seems to be missing? php53-tidy.
Restart Apache (service httpd restart). Update WordPress. If you miss on restarting the web server, it won’t detect the newer PHP install and WordPress will just show you a magical message as follows: “You cannot update because WordPress 3.2.1 requires PHP version 5.2.4 or higher. You are running version 5.1.6.”