@dragomaster,

Just as a warning, the web interface for Deco is not as thorough as the Deco App and you will need to use the Deco App to configure some features. 

You will also need to follow this FAQ, specific to Decos - as the address is actually tplinkdeco.net

I would recommend using the Deco App as it is a reliable form of changing your device settings, whether on your network or not. Furthermore, almost all FAQs and Guides will revolve around the steps used in the Deco App, rather than the WebUI. 

To change the admin password, you should only need to login with your TP-Link ID and then the router will use these credentials for login.

  @dragomaster,

The goal is to link your Deco Network to Your TP-Link ID, which will change the admin login for the router to that of your TP-Link ID. Normally when setting up the Decos through the app, the account will be bound by what was logged into on the app, if it was skipped in the web interface, there should be an option to link - otherwise, make sure that the Deco app is indicating that your TP-Link is the owner.