The registry path should be: (There may be slight variations in the path titles - 16,for example, could be 15)
HKEY_LOCAL_MACHINE\software\policies\microsoft\office\16.0\common\officeupdate
You should see the key, or, make one Enter Value name\HideUpdateNotifications
Value type Reg Dword
Enabled value 1
Disabled value (which you want ) 0