Follow these steps to uninstall PHP from IIS.

1. Go to C:\Windows\System32\inetsrv\config and open the applicationHost file in a text editor such as Notepad or Notepad++
2. Delete the following text from the applicationHost file:

<application 
fullPath="C:\Program Files\iis express\PHP\v7.0\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\v7.0" />
    </environmentVariables>
</application>

3. Also delete the following text from the applicationHost file:

<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" 
/>

4. Go to C:\Program Files\PHP, and delete the version folder.