Hello,
Php handlers tells that how PHP is loaded on the server. There are multiple handlers that can be used for loading PHP: CGI, DSO, suPHP, & FastCGI.
Using WHM control panel you can simply change the php handler. Here are the steps to do the same.
1. Login to WHM
2. Go to Home >> Service Configuration >> Configure PHP and suEXEC
3. Select the php handler from drop down list shows in front of php 5 handler
4.Save new configuration.
That's all. Enjoy !!