For example, I will update D-Link DIR-615 with the old firmware 1.0.19 to version 2.5.4.
I will describe the steps in steps:
1) Download the new firmware from the official site
2) Open the settings of the router by typing the address http://192.168.0.1 in the browser (maybe 192.168.1.1) and enter the standard login – admin, the password – admin.
3) In the interface that opens, click on the “Advanced Settings” at the bottom and in the “System” block click on the arrows “>>”, then select “Software Update”. In the window that opens, click “Browse” and select the previously downloaded firmware file, then click “Update” to start the update process.
Wait until the update is complete, usually 2-5 minutes. At the end, the router will reboot.
On the test, the settings remained unchanged, which means that the D-Link DIR-615 router can be flashed remotely.