How to disable the “Get Windows 10” icon shown in the notification area?

1. Run regedit.exe as an adminstrator.
2. Open HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\ and create Gwx key in it.
3. Create new dword value, named DisableGwx in it.
4. Edit it and set its value to 1 (00000001).

Restart Windows to see the effects.

This registry key will stop GWX from displaying:

[HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\Gwx]
"DisableGwx"=dword:00000001

reg add HKLM\SOFTWARE\Policies\Microsoft\Windows\Gwx /v DisableGwx /t REG_DWORD /d 00000001