Gergith, your how-to worked like a charm.
I followed your instructions for upgrading step by step, only difference was doing it on a Linux system. I replaced the 4GB µSD by a 16 GB Class 10 one.
What happened during the first start was that the blue light came up at boot, but nothing further happened, and I was concerned I had bricked it by destroying something sensitive.
I plugged it to my laptop, it booted properly and the screen came up with a 'found computer' notice, connected with it, and charged the battery. From then on, it worked normally again. Maybe the battery was just low, so I would recommend doing that with a fully charged reader.
Another point is that the 16GB class 10 card is much slower than the 4 GB card, which initially I thought was due to the larger size. Now I read in the forum that class 4 cards have smaller block writes (As DNSB writes in the 'SD Card Performance - some discussions and info' articles on the List of Tweaks / Hacks / Mods.
. Apparently this is due to the fact that the class 10 cards are optimised for cameras with larger files to be stored.
I ordered a 32 GB class 4 µSD card now and will test how that that one works.
Thank you very much again, Gergith