For risk takers ...

We tried replacing the screen, but we do not manage to disassemble the phone because the supplied screwdriver is too fragile.
In the end, impossible to disassemble all the screws without finding a good and true screwdriver.
Then there is no question here of the screen, without the frame to match. So, do not be afraid to definitively destroy the old screen to detach from the holder. Attention, the media is that the front part of the phone and is very thin. If it breaks, it's all screwed up ...

So, as we had two Lumia 520 to fix (they seem quite fragile on that side, but the side out of luck also played ...), I went to see a specialist who replaced 10 minutes the screen a first portable, and took 20 minutes to take charge (recovery of the support forces) to install me about the comment screen.
The editor was very nice and I only took 10 for mounting of the screen and 50 the first Nokia phone with screen. So 30 one side with mounting difficulty and 50 other with guaranteed editing ...

Otherwise, installed display, the phone works, but sometimes random reactions (no consideration of contact on the screen, or on the contrary, considered too supports ...). In short, if it is to do again, I would resume the on-site repair option.