That was done during summer 2016 and fully tested during 12 months for problems. None were found so the procedure below is quite secure. If you read this and you are about to update your PHP file to use mySQLi calls the best is to prepare you work thoroughly in advance. Check which functions are used and what is the mySQLi equivalent, the name use to be the same but with a mysqli_ prefix instead of mysql_ however most function calls require more parameters to be passed and they can be in reverse order.
List of MySQL functions to update (in lm_functions.php):