From the same Settings page where you can enable Narrator:
To turn Narrator off, press and hold the Volume Up button, then press the Start button.
For more information, see Using Narrator on your phone.
You can control the speed of the narrator using a slidebar.
Go to Ease of Access -> Narrator.
You could see a slider under the speed option.
Drag the slider to increase or decrease the speed of the narrator.
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!