in the engine bay undo the pipes to the heter matrix
then the 2 screws that hold the tab in place otherwise the matrix won't come out at all
driver and passenger side sill covers next
then kick panels
then the drivers side lower dash
then the passenger side lower dash
then you can see what you need to do
pop the cable controls off the adjusters
unscrew the clamping plates for the cables
undo the 2 13mm nuts that hold the heater box in place
slide the whole lot out
remove 2 screws that hold the matrix in the heater box
refit as you remove

you may need to remove the centre console if it's not been out before and the rear under seat heater pipes are a bit of a bitch to do as well
and yes, try and keep your temper and don't do it if you think you need the car in the next 10 minutes either