how to and when to divide a large Gunnera plant

The BBC page indicates to do it March - May.

http://www.bbc.co.uk/gardening/plants/plant_finder/plant_pages/358.shtml

I'm guessing the method is the usual one: prepare new planting holes, dig up plant, use spade to chop it into however many parts you want - if huge then remove old woody bit in middle, always ensuring there are growing tips still available, then replant.