Never done this either but the diagram i have shows....
remove radio
on the row of switches under the vents there are screws hidden at each end under the half plastic trims.
then it shows removing the ash try and screws behind the ash tray.
then shows the centre section of dash removed.
the vents come out with the middle section of the dash but i would have thought there would be air ducting and cables to diconnect. diagram dont show any further so in the dark about the rest. i think to change the vents they have to come out the back. this is all i can tell you sorry.
clobak