The PHP Case Converter collection helps changing the cases of existing texts.
<?php
require_once("CaseConverter.php");
$converter = new CaseConverter();
$input = "The quick brown fox jumps over the lazy dog";
$converter->convertToUpperCase($input); // THE QUICK BROWN FOX JUMPS OVER THE LAZY DOG
$converter->convertToLowerCase($input); // the quick brown fox jumps over the lazy dog
$converter->convertToStartCase($input); // The Quick Brown Fox Jumps Over The Lazy Dog
$converter->convertToCamelCase($input); // TheQuickBrownFoxJumpsOverTheLazyDog
$converter->convertToSnakeCase($input); // The_Quick_Brown_Fox_Jumps_Over_The_Lazy_Dog
$converter->convertToKebabCase($input); // the-quick-brown-fox-jumps-over-the-lazy-dog
$converter->convertToStudlyCaps($input); // THe QUiCk BRoWn FoX JUMps oVeR thE LazY dOG
$converter->invertCase($input); // tHE QUICK BROWN FOX JUMPS OVER THE LAZY DOG
Get more information and online tools for this implementation on https://en.toolpage.org/cat/case-converter