You need to firstly remove the wood (or metal) centre console trim,

The pictures below are for the pre MY2005 facelift, however the procedure is the same on newer cars except that you must open the cupholders, remove the front piece and close them again.

On MY2009 cars to remove the COMAND you must also remove the airvents above to access the screws that hold the top of the COMAND unit.

 

Firstly remove the trim either side of the centre console.

Lower the seats to the lowest and most rearward position to give best access, and then remove the trim which just pulls off from the centre console and then slides out from the dashboard. Put your fingers under the trim (above the carpet) in the middle and pull gently to release the middle clips, work your way backwards until all the clips are released and then pull the trim out (pulling to the rear of the car away from the dashboard).

Here is a picture of the trim removed, circled are the hooks that hook into the dashboard, you can also see all the clips that hold the trim to the centre console and the other two metal clips that lock it into the dashboard.

Now unscrew the 3x TORX TX20 screws on each side that hold the wood/metal trim to the centre console. The screws are quite long and the screw at the rear end is recessed so a torch / flash-light is useful.

Once that is removed, remove the gear selector knob - move the gear selector to N (ensure the parking break is on and the wheels are chocked), pull up the leather gaitor, rotate the knurled nut 90 degress anti-clockwise and pull the gear knob upward. If the car has keyless go you must not twist the gear knob or you may break the pins from the start/stop switch that plug into the top of the gear selector shaft. On non-keyless-go cars, twisting the knob as you pull upward helps.

On MY2005 onward cars, open the cupholders and remove the front panel and close them again - this allows the two tabs at the top of the centre console trim (that cover the cupholder screws) to come forward without hitting the cupholders.

Ensure that the ash-tray is closed (remove the insert), and you can then pull up the trim, from the rear, by pulling on it through the hole left by the gaitor.

Pull the whole trim out further by pulling it away from the audio/COMAND unit, the ash-tray does intefere with the gear selector surround, so take care.

Once the whole trim is released you should disconnect the 3 cables (one pulls straight out, two are on rotating clips) from the airconditioning unit, the cigarette lighter power (pulls out at 90 degress to the body of the cigarette lighter) and the purple connector on the gearbox mode selector (W/S, W/S/M button). Also disconnect the two plugs to the roof / mirror selector switch if you want to remove the whole trim, but you can just lay it to the side if just removing the audio system.

You will now see one screw (red in picture below) each side of the cup-holder and two screws (blue) each side of the audio unit, which you should undo and remove to remove the audio unit.

On MY2005 - MY2008 the COMAND is held in by the cup-holder screws and two catches underneath that need to be relased.

On MY2009 onward COMAND is also held in by the cupholder screws but there are two additional screws that screw into the top of the COMAND. To access these screws the vents above COMAND must be removed. This is done by removing the speaker grill above them exposing two screws, undo those screws. There are then two hook catches (one at the bottom of each vent) which can be seen through the vents - these are best released with the Mercedes pulling hook tool which will release and pull the whole vent forward.

When re-assembling ensure that the wiring does not get caught in the ash-tray mechanism, and that all wires are plugged back in again.