Zyxel router (updating firmware correctly!) ...

At the beginning of the year, another Zyxel P-2602HWL-D1A firmware was released.
For relatives and friends there are several such devices.
I asked one friend to update the firmware. It turned out that the person was reading the documentation, but the last time after the “update” I had to carry
device in service. I looked into the documentation - and the truth is, more or less correct.
update procedure, there is not explicitly described at all ...
Interestingly, this is specifically done so that the people more devices spoiled and in the service did not forget the way?

I describe the scenario of "correct update" (tested on devices of the P-2X series, but probably suitable for other devices from this manufacturer):

1. If after the update we are too lazy to remember a lot of information embedded in the device (provider login and password, connection settings, DDNS, Time, SIP provider settings, notebook, etc.), then we save the configuration to a separate file.
2. Reset the device to factory settings ("factory reset").
3. Go to the device, select the file with the new firmware - and update, go ahead!
4. (!) We go to the device and again reset the device to factory settings ("factory reset").
5. We go to the device, and with the help of the configuration file (from the first step) we restore our settings. Those who ignored point 1 can manually tune the device (for taste and color ... well, who likes it ..)

If it helps at least one person, then I knowingly spent five minutes to print this text .. :) ...