1. Enable the REMI repo and Upgrade software
yum –-enablerepo=remi install mysql
The reason for using install mysql is that the yum software utility will install/upgrade all dependencies to ensure that all the software pieces work together. It will also upgrade all the related PHP packages (e.g. php-gd, php-devel, php-mbstring, php-cli, etc) from version 5.3 to 5.4
2. Run Mysql Upgrade
mysql_upgrade -u root -p
3. Edit /etc/httpd/conf.d/php.conf
Replace:
<FilesMatch \.php$> SetHandler application/x-httpd-php </FilesMatch>
With:
AddHandler php5-script .php
I also had to run the following to get phpmyadmin to work
yum --enablerepo=remi install php-mbstring
How To: Virtualmin CentOS Upgrade PHP 5.3 to 5.4