To check what version of PHP you are using; see How to Check My PHP Configuration and Version
In order to make use of PHP5 you can either use the .php5 extension on all PHP files or alternatively modify the htaccess file.
The .htaccess file is located in the root directory of your hosting account. It is a hidden file, so please ensure
your FTP software allows to view hidden files, or just access this file via CPanel’s “File Manager” interface. Simply add the following line to the .htaccess file:
AddHandler application/x-httpd-php5 .php