METHOD #1) GPEDIT.MSC
Start / Run / gpedit.msc
Computer Configuration / Administrative Templates / Windows Components / Windows Update
No auto-restart with logged on users for scheduled automatic updates installations: Enabled
Re-prompt for restart with scheduled installations: Enabled, wait period (minutes): 1440

METHOD #2) REGEDIT
HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\WindowsUpdate\AU
DWORD (32-bit): NoAutoRebootWithLoggedOnUsers=1

ALTERNATIVE METHOD (disable in start up)
HKEY_LOCAL_MACHINE>SOFTWARE>Microsoft>Windows>CurrentVersion>Run
String Value: "Disable Windows Update Restart Notification" = "Cmd.exe sc stop wuauserv"