I've just updated my RRS's satnav now the car's here in Oz and it's as simple as Stu suggests, all you need do is put a new DVD in the player under the passenger seat and it'll run through the update itself, you just need to make a few selections at the end. The only hindrance is the fire extinguisher mounting, you'll need to slide the seat forward & back whilst ejecting the DVD as the mounting bracket covers the DVD player's slot.
You may find that if the nav's previously been set to allow programming on the move that the function disappears with the new disc, you'll need to get it re-enabled again. It has done with mine, but that may also be to do with the fact it's gone from the UK DVD to an Australian one, I'm not sure if it's a function you can have here. I'll soon find out though...