I do as the user manual says and press "Managed Mode" button to get into unmanaged mode and then press "Managed Mode" button again for managed mode. This should reset the device to factory defaults and username "Admin" with no password.
However, the device resets (I think) and I can access the web console from IP 192.168.2.1, but the username and password doesn't work.
Maybe the device doesn't reset after all. Or the username/password has been changed in some firmware upgrade? What should I do to get into management of this switch?