I have never removed the switch myself, but have instructions as follows - It would seem that one must first remove the instrument cluster (dials), so the switch might be accessible from within that par of the dash. Disconnect the negative battery terminal , Remove the steering wheel (after the horn) and pry away the instrument cluster. You might need to disconnect the speedo cable and other connections to get proper access to the ignition switch, but I can't be certain.
Take big breath.
The ignition switch is located furthest from the driver in an assembly which incorporates the steering lock. The switch will have an electrical plug connected to it. Remove this plug, keeping in mind its orientation for reattachment.
There are some small screws that attach the switch to the assembly (?not sure how many?) Use a small screwdriver to remove these, and the switch should come out.
Install new switch. Reassemble other stuff. Use money saved to buy bottle of champagne and toast to the health of your car (+/- partner).
Hope this helps. These instructions should cover all 107 chassis models, but I can't be certain, as they were given to me for my car specifically (1980 450sl). All the best in your endeavor. Daniel.