Like infinity said they are only accessible from the rear which is a really big pain due to the fact of having tor remove the dash and some other bits as well!
I unfortunately broke a few blades on one of my central are vents with a air freshener unit that clamped to the air vent!
I did everything to try and avoid removing the dash including first removing the hazard and rear window heater switches to access the offending vent which gained me access to only one side of the vent which of course was connected to the air ducting making it impossible to access the vents other side!
At the same time I was scrapping a donor 2002 1.4SE+ so I had practiced removing parts from that car which gave me a bit of experience and a invaluable insight on opening the"Pandora's Box" of the task of removing the dash and other associated bits!
After the nightmare of dash removal on the scrapped Micra I decided to adopt a different approach on my good 2002 1.4SE+ so I broke up the rest of the broken vent carefully removing all bits (to save the bits rattling in the air ducting forever more). I then lubricated the side locating logs on the replacement vent with fairy liquid and proceeded to refit the vent from the front of the dash face. After what seemed an eternity of jiggling the vent at every angle imaginable I managed to locate it into it's correct position without breaking it
JOB DONE lol!
I will try and find some pics of the above task which still gives me nightmares lol!
Cheers
Andy