SharePoint 2013
Central Administration à Upgrade and Migration à Check Product and patch installation status
Office Web Apps
Open PowerShell as Administrator on Office Web Apps Server
(Invoke-WebRequest http://officewebapps.com/m/met/participant.svc/jsonAnonymous/BroadcastPing).Headers[“X-OfficeVersion“]
For Version Comparison
SharePoint 2013 Build Numbers by Todd Klindt