How do I open Logitech Cordless Click! Plus Rechargeable Mouse?

I have this mouse for a lot of years. I don't know when it happened (somebody else uses this mouse ;-), but the wheel does not scroll vertically any more, in any software. I tried an other mouse (with a wheel) of a different type on the PC: it works.

I'm almost sure it's not a driver problem, because the PC is an Ubuntu system, it worked immediately without having to install anything on the first day, 5 years ago, and I'm *almost* sure the system can't regress to forget how to use the wheel. But I know somebody using such a mouse, and I plan to borrow it for a couple of hours and see how this other one works on my different PCs (5 at home ;-)

Probably, some component is tired inside my mouse, but I don' know how to open it safely to reach the circuit board.