Use winver.exe
Useful link: https://social.technet.microsoft.com/Forums/office/en-US/19b1fe0a-3267-4f2c-9e9d-42735bc81a36/how-can-one-quickly-tell-if-a-server-is-2008-or-2008-r2?forum=winservergen
Use iisreset
Useful link: https://msdn.microsoft.com/en-us/library/ms957500(v=cs.70).aspx