Trying pulling it out and removing the power plug from the back. Make sure you have the code first though. If you don't have the removal tools then just call in at a car hi-fi place and ask nicely...
W203s do not have a code for the HU... I enquired about this as I never recieved any pin code with my documentation on any of my cars upon the handover from the Stealerships.
If the pin code did apply to your car (which it does not) then you could obtain the code from DC Customer Services but would have to provide ID and proof of ownership etc. first!!!
Yes you need the two keys/tools which are inserted into the vertical side slots on the HU in order to release the unit. You could buy these from Stealership Parts Dept or if find a friendly Staelership they may even send someone out to do it for you as it only takes seconds to do.
