Hi @Eycan Nural, welcome on the forum. You are following the correct steps, but it doesn't work. You mentioned you get an error. What error do you get? Can you tell us more?

In our Knowledge Base we have an article in logging in to the Box, the bit in yellow gives extra tips when it doesn't work right away: Inloggen webinterface KPN Box 12.

It is in Dutch, but with Google Translate it can help you.

Hello @Eycan Nural please try this:

https://192.168.2.254

@Jasper  http://192.168.2.254/2.0/gui/#/login via this link I always get “could not change password” error and this site is the only one that I can login and also I could not change the page from password changer on this site.

So if I understand corectly, logging in to that site does work? Where do you get the error you can't change the password? Is that on the login page, or do you mean in the Wifi settings? If it helpt you can share screenshots of what you see. Make sure to hide private information in them, like your ip address.