if you're unsure what php.ini is being used, create a new file in your webfolder, name it
phpinfo.php for example , with the following content
then open the url in your browser (http://www.example.com/phpinfo.php). it will show the path to the php.ini being used.
when you have identified the correct file, make your desired changes, and be sure to remove the leading ; in case there is one to activate the setting.
restart apache and reload the phpinfo page, your changed setting should now show up. if it doesn't, make sure you don't have a .htaccess file in your webroot that overrides php settings.