On-demand install script for Windows Update clients

You can safely use the VBScript below, from any server console, it immediately downloads and installs all approved patches then reboot if required.

Set fso = CreateObject("Scripting.FileSystemObject")
Set objAutomaticUpdates = CreateObject("Microsoft.Update.AutoUpdate")
objAutomaticUpdates.EnableService
objAutomaticUpdates.DetectNow
Set objSession = CreateObject("Microsoft.Update.Session")
Set objSearcher = objSession.CreateUpdateSearcher()
Set objResults = objSearcher.Search("IsInstalled=0 and Type='Software'")
Set colUpdates = objResults.Updates
Set objUpdatesToDownload = CreateObject("Microsoft.Update.UpdateColl")
intUpdateCount = 0

For i = 0 to colUpdates.Count - 1
 intUpdateCount = intUpdateCount + 1
 Set objUpdate = colUpdates.Item(i)
 objUpdatesToDownload.Add(objUpdate)
Next

If intUpdateCount = 0 Then
 WScript.Quit
Else
 Set objDownloader = objSession.CreateUpdateDownloader()
 objDownloader.Updates = objUpdatesToDownload
 objDownloader.Download()
 Set objInstaller = objSession.CreateUpdateInstaller()
 objInstaller.Updates = objUpdatesToDownload
 Set installationResult = objInstaller.Install()
 
 Set objSysInfo = CreateObject("Microsoft.Update.SystemInfo")
 If objSysInfo.RebootRequired Then
  Set objWMIService = GetObject("winmgmts:{impersonationLevel=impersonate, Shutdown)}!\\localhost\root\cimv2")
  Set colOperatingSystems = objWMIService.ExecQuery("Select * from Win32_OperatingSystem")
  For Each objOperatingSystem in colOperatingSystems
   objOperatingSystem.Reboot()
  Next
 End If
End If

Source : Best Practices in Architecting and Implementing Windows Server Update Services (WSUS)