For example, I will flash the D-Link DSL-2500U modem with firmware 1.0.47 for version 1.0.50.
I will describe the steps in steps:
1) Download the new firmware from the official site
for Annex B from here
2) Open the router settings by typing in the browser the address http://192.168.1.1 (maybe 192.168.0.1) and enter the standard login – admin, the password – admin.
3) In the interface that opens, select “System” – “Software Update”, then click “Browse” and select the firmware file previously downloaded, then click “Update” to start the update process.
Wait until the update is complete, usually 2-5 minutes. At the end, the modem will reboot.