Php code compatibility version 5.2 to 5.4

I'm currently using a PHP Version 5.2.5. I want to upgrade my php to PHP version 5.4.35 and my apache 2.0.5(no ssl) to apache 2.2.25 (open ssl). Does my code compatible with the current and the latest version or should i rewrite my code to be compatible? Help.. pls Thank you..