Open your registry and find or create the key below.
[HKEY_LOCAL_MACHINESoftwarePoliciesMicrosoftWindowsWindowsUpdateAU]
Create a new DWORD value called „UseWUServer” and set it to „1” to use custom update servers or delete the value to use the default Internet site.
Then open the key
[HKEY_LOCAL_MACHINESoftwarePoliciesMicrosoftWindowsWindowsUpdate]
and create two new string values called „WUServer” and „WUStatusServer”, set these values to the names of the custom update servers (e.g. „http://intranetupdate”).
Restart Windows for the changes to take effect.