To easily upgrade your WAMP installation, go to the WAMPServer Backup Repo and download the Wampserver update x.x.x (whatever the latest version of WAMPServer is) from the second section of the page titles Wampserver Updates. That will upgrade the WAMPServer code, and nothing else. All code/databases will remain just as they were before.
PHP (PHP: Hypertext Preprocessor) is a popular open source general-purpose server side scripting language that is especially suited for web development and can be embedded into HTML. For more, check php.net