Changing SIM card on NTT DOCOMO

Quick note on changing/activating a new SIM card on NTT Docomo...

...  when switching to a new phone

So I changed my "Smart Phone" from nasty domestic to nasty Korean brand.
I ordered everything through the Docomo Online shop, which was a challenge by itself (J-IT Mess).
 The new phone arrived with a new SIM in the right physical form factor (Nano), I thought there would be some kind of automatic or semi-automatic switch-over, but apparently that was not the case.
 I tried my luck reading through the instructions on how to do this online, but I could not get this figured out. I cannot see any point in the "Online Contract Change" or however one would translate this.

After calling support, all that needed to be done was:

1. Call 1580 from the new phone (which has the new SIM inserted obviously).
2. Then enter the Network-Anshin-Bango followed by #-sign. 
3. Then confirm with '1' and '#' and voila - done. 

Beats me, why they do not put that in the huge mess of various instructions.
So maybe this helps somebody.