The current default is PHP 5 and this is best for Joomla, but if for some reason you need to change to PHP 4 it can be done using the PHP Configuration in cPanel.This affects the entire account.
To override the default and use PHP 4 for only some files add this line to a .htaccess file in the same folder as the files to be affected.
AddHandler application/x-httpd-php4 php
for PHP 4, or
AddHandler application/x-httpd-php5 php
for PHP 5.
