Sounds like your well prepared, I personally place the bottle, Valve first into a cup of boiling water for a min or two, My tool is the spanner type which I apply and using a piece of wood give a sharp wack or two on the spanner anti clockwise to undo the thread, I hold the bottle in my hand, Vice is ok as well if padded,
You are only softening the locktight with the heat. There is already a seal between the bottle and the valve, Repeat if not hot enough. Don't forget to apply locktight on your new valve thread when fitting the new one. Col.