I have a Nokia Lumia 520 phone with Windows 8.1 upgrade. tried holding the Volume Up button for three seconds and simultaneously pressing the Start button as suggested, but the narrator will not let go, therefore I cannot access the setting to disable it! Now what!
I went to the ATT store here in town. The representative there searched for an alternative solution for me. He was able to hold down the upper part of the volume button for 3 seconds and then double tap on the windows symbol on the phone, but not simultaneously. And it worked!