no diy! switching the lsd unit is easier than switching the gearset.
you need some special tools, adjustment ring sets and the knowledge how to measure it in.
here i took some pics of a c63 amg gearset change i did recently:
http://www.limitedslip.de/service/einbau_c63.html
the m3 axle is a little different but the work and tools are more or less the same.