Steps (Use sudo only if required)
1) Remove OLD Apache
sudo service httpd stop sudo yum erase httpd httpd-tools apr apr-util
2) Remove OLD PHP
sudo yum remove php-*
if it´s a clean installation start from here:
3) Install PHP 5.6 (Apache 2.4 will be automatically installed with this)
sudo yum install php56
4) Make sure all the required PHP extensions are installed
yum list installed | grep php
5) If not then install them using
sudo yum install php56-xml php56-xmlrpc php56-soap php56-gd
6) To list the other available php extensions
yum search php56
7) PHP 5.6 MySQL extension (Assume you have already installed MySQL)
sudo yum install php56-mysqlnd
(NOTE: it is not php56-mysql)
8) Start / Restart Apache
sudo service httpd start sudo service httpd restart
9) Check the version
php -v httpd -v