I will describe the steps:
1) Download the new firmware from the official website
2) Open the router settings by typing in the browser address http://192.168.1.1 (can be 192.168.0.1) and enter the login/password.
3) In the opened interface, open the menu “System Tools“, choose “Firmware Upgrade“, in the opened window, click “Browse” and select the previously downloaded firmware, click “Upgrade” to start the upgrade process. We are waiting for the completion of the process for about 2-5 minutes.