How to run PHP-5
By default, all our servers are configured to run PHP-5 (which is the latest stable version). All your .php files will automatically use PHP-5 by default. No special action is required on your part to run PHP-5 scripts on our server.
How to run PHP-4
If you would like to use PHP-4 for your scripts, there are two options:
1) Rename the files that require PHP-4 with the .php4 extension (as opposed to .php). This is useful if you just want to test a few files under PHP-4.
2) If you would like ALL your files within a specific directory (for example, public_html folder) to use PHP-4, then create (or append to a current) .htaccess file the following line. Make sure to work with .htaccess file located in that specific directory.
AddType application/x-httpd-php4 .php