Want to call mysqli.php instead of mysql.php

Hi guys, i am getting depriciation error(Depricated mysql connect() error:- This error will be removed in future. Use Mysqli or PDO) in my opencart. So I need to call mysqli.php instead of mysql.php. From where can i do it,. Can anyone tell me the path of that file

open config.php file and admin/config.php file and see this line

define('DB_DRIVER', 'mysql');

change it to mysqli for use mysqli