This is done on the handset itself.
- Step 1 Unplug the power cable from the phone and then plug it back in.The phone begins its power-up cycle.
- Step 2 While the phone is powering up, and before the Speaker button flashes on and off, press and hold #. Continue to hold # until each line button flashes on and off in sequence in amber. On some handsets, this does not happen, however, after holding the # button down (for about a minute or two proceed to the next step)
- Step 3 Release # and press 123456789*0#.
You can press a key twice in a row, but if you press the keys out of sequence, the factory reset will not take place.
The display will change and indicate that it is loading new code, once complete it will again reset and eventually display a login screen.