Changing light switch - 89 Audi 100

[Martin W. N. Suryadarma]

Hi, what tools do I need, and what are the procedures to replace a light
switch for my Audi?
Here is the condition, side markers are fine, high beams are fine, but low
beams don't turn on. Checked the fuses, all ok. So last resort is
headlight switch. 
It's a 1989 Audi 100, I don't think it has airbag, but if you think
otherwise, please let me know. On the left side of the steering column,
there are two switches. The long one for signal + cruise control + high
beams, and the short one for side marker + headlights. I am trying to
replace the short one. 
Do I need the 22mm or 24mm socket? And how do I open the thing apart?
Thank you very much beforehand.

An Audi Newbie,

Martin