Don't factory reset, it just screws the box up and you will need to reflash.
If you're planning on flashing the box anyway, just flash it. It will wipe any existing data. (as Andy say, backup your line).
Ok thankyou for that, I have 2 zgemma boxes connected to my virgin media modem, can having to many devices connected to it cause it to freeze as I seem to be having this issue and if so how can I get around this? Thanks
All the factory reset option does is wipe the user area (this is where your line is also stored). It does not return the receiver to factory standard, you would need to reflash the original factory image for that, something the zgemma does not actually possess.