First of all why do you need to hard reset before updating the firmware. I guess there is no need to. Just backup your phone contents like contacts, messages, settings etc.
If you still want to hard reset then do the following
1. Turn off your phone
2. Press the green, red and camera button simultaneously and restart the phone while the buttons being still in pressed state.
3. You should get the screen which will prompt you to set city, time etc. Your phone is hard resetted now
Warning: You will loose EVERYTHING on your phone when you hard reset so please backup phone contents before attempting this