GWX is a great tool for removing the Windows 10 upgrade notification:

Alternatively, our staff usually will remove/uninstall the KB3035583 Windows Update, refresh the Windows Updates (before rebooting), then hide the update, and finally reboot.  The following page also includes some regedits that they've had to do:

Ideally, we recommend using GWX as that is the easiest way to remove all notifications to install/upgrade to Windows 10.