You take out the wooden centre console slowly and remove the switch from the underside so as not to damage the veneer.
Depending on the year of your car the Radio and Aircon control units may require different tools to remove and some of the clips at the back vary - the video makes it look very easy - my console required a little coaxing - extra care when pulling it out and pressing it back in.
In case you don't know..There is a series of these videos very handy on Benzworld in the stickies I think....
This is for an older R129....
I have done this a few times so feel free to pick my limited brain - (I would know nothing but for the other forum members expertise and help)