Open the web browser and in the address bar type in: http://192.168.1.1 or http://192.168.0.1 or http://tplinklogin.net.Then press Enter.
The LAN IP changes by model. Please find it on the bottom label of the product.
Type the username and password in the login page. They are both admin by default.
Select System Tools->Password on the left side to open the configuration page.
Type the old and the new username/password, then click Save.
Note: Do not forget the new username and password. If you forgot them, you need to reset the router to factory default setting.