I could only update the FW with Lacie Network Assistant, there was no option to update from NetworkSpace2 (as mentioned in the hands-on),
so I have updated first the Assistant from 1.41. to 1.43 on my iMac.
Thereafter I have stopped the services on the NetworkSpace2.
Then, during the update from stage 2 --> 3 my iMac asks for the admin password.
Stage 3 does indeed take a while, just take a cup-of-coffee.
So I'll think for Windows users you should have admin rights, before you update the FW (just my thoughts).
I can confirm that there is no built-in option to update software in NetworkSpace2 mentioned in update instructions. Also, I have disabled all services (multimedia, FTP) before the update. Windows-version of the Network Assistant asks for admin-password right after pressing Update NAS..-button in configuration wizard, so it's not a permission issue, I think.
Thanks guys for the support. I have received few responses from LaCie-team already but so far their only advice is to return the device back to LaCie for fixup.