This are the procedures. if you do have right tools nothing special (set of molegrips and a hammer!) , but if they are very dificult to disconect may be you need to force them.I would call someone with experience in that case.
Some pics of workshop in 617A. File in PDF.
PDf file showing same.
http://www.benzworld.org/forums/attachments/g-class/154771d1198459975-problem-removing-glow-plugs-glowplug.pdf