The MultiPHP Manager enables you to change the version of PHP running on your account, even allowing different versions of PHP to run under your account, such as on Subdomains or Addon Domains.
If you wish to see or change what version of PHP is enabled globally on your account, follow the instructions contained in How do I change my version of PHP?
However, if you wish to view or change the version of PHP that is applied to a specific area of your account, such as a Subdomain or Addon Domain you would use the MultiPHP Manager.
You simply tick the box for that specific area and then select the appropriate version of PHP and click "Apply".
Please remember that you may need to check What PHP Extensions are enabled in my version of PHP? and change them for each and every version of PHP you wish to use within your hosting account. Similarly, you can also change the PHP Options used for each version of PHP.