Following on from the answer by Dan, the applicationhost.config file is located at C:\Windows\System32\inetsrv\config, and the sections are detailed in it:
Find following entry (or similar entry) in applicationhost.config file and comment it or delete it.
<application fullPath="C:\Program Files\iis express\PHP\v5.2\php-cgi.exe" monitorChangesTo="php.ini" activityTimeout="600" requestTimeout="600" instanceMaxRequests="10000"> <environmentVariables> <environmentVariable name="PHP_FCGI_MAX_REQUESTS" value="10000" /> <environmentVariable name="PHPRC" value="C:\Program Files\iis express\PHP\v5.2"/> </environmentVariables> </application>
Find following entry in hanlders section and comment this as well or delete.
<add name="PHP52_via_FastCGI" path="*.php" verb="GET,HEAD,POST" modules="FastCgiModule" scriptProcessor="C:\Program Files (x86)\iis express\PHP\v5.2\php-cgi.exe" resourceType="Either" />
This is simply the configuration file sitting behind the IIS Manager console, the same result can be achieved by opening the IIS Manager Console, and then opening the FastCGI settings and deleting the reference to PHP 5.3, and then opening the handler mapping section and removing the mapping for PHP 5.3.