How do I upgarde from PHP 4 to PHP 5, and what changes are need to be made ?

You can upgrade from PHP4 to PHP5 by recompiling PHP during the Apache build process. You can start the Apache build process in WHM under Software >> Apache Update, or on the command line as root using /scripts/easyapache.

You'll need to make sure that the PHP programs and scripts you wish to run are compatible with PHP5. You can also choose to run both PHP 4 and 5. For more information on running both versions of PHP and the Apache build process, see http://www.cpanel.net/support/docs/ea/ea3/.