Tweeters

Do you access these through the panels at the end of the dash or does the little grille lever up

Levers up, gently

VERY gently otherwise you'll knacker the surrounding trim. I recomend a trim lifting tool, kind of like a screwdriver with the end bent a little and a V shape in it. Works a treat

or just bang it out from behind.

As ^^^ says, but do it on a warm day or the retention tabs will shatter. Or get the Hairdryer out

I just saw the extensive guide for tweeter swap in the Guide-section.
I could'nt reply there as it's locked, but here's another - simpler - way of doing it, whilst retaining the factory look (and keeping a few more thiefs out):

http://sfk.ibk.se/depa/showfile.php?carpic_no=2170&type=picture

You simply glue it on, I used a hotgluegun. Done!
Huge improvement of the sound + stereo ambience.

Cheers / Per