First, do not edit php.ini, instead add a file to
called something like php_ini_local.ini, for instance. Place parameters you would like to customize like upload_max_filesize in there, and they will take precedence over those in the php.ini file(s). And this way php.ini will in future also upgrade gracefully to newer versions without manual intervention.
To test parameter changes (before and after) the simple way, use PHP CLI in a terminal:
# php -a Ctrl-d