We can change all characters to lower case by using strtolower. The following code is an example.
$string = 'I am ThEt NainG WiN!';
$string_low = strtolower($string);
We can also change all characters to upper case by using strtoupper. The following is an example.
$string = 'I am ThEt NAInG win!';
$string_up = strtoupper($string);