@Alexandre. None of above worked. However, I tried additional point - simply I go to details of M5 and selected "remove", I was warned that my coverage will be down - but I have confirmed. Then... I...

@Alexandre. Sorry, maybe i was not clear - I am not saying that the option to change is missing. I meant that I am not able to choose Deco M4 as main device. Please see my config as for now - there...

Originally I have bought set of two M4 devices. Some time later I have got Deco M5 and then I have added it to my network. Then M5 was set as main deco. One of M4 device was removed from network. Now...