I use NaviFirm and Phoenix method. If it's your first time I recommend you watch this -

http://www.youtube.com/watch?v=Zeet3k1_330

Keep the vid open, pausing it as you go through each step.
You should give yourself about an hour, that should be enough. But do not rush it - be certain of what you are doing at each stage.

Edit - and don't worry about the Symbian reference - this method works fine on my N9