For example, I will update the firmware in the TP-Link TL-WDR3600 V1 router.
1) Let’s see the new firmware version on the official website
https://www.tp-link.com/ru/support/download/tl-wdr3600/#Firmware
2) Open the router settings by typing the address http://192.168.0.1 in the browser and enter the standard login – admin, password – admin.
In the menu, select System Tools – Firmware Upgrade, where “Firmware version:” let’s see the installed version, I had “3.13.23 Build 130527 Rel.59702n”, and on the official website I found and downloaded the version “TL-WDR3600_V1_150605_RU”.
3) To start the update, click the Browse button, select the previously downloaded firmware file with the *.bin extension (I had wdr3600v1_ru_3_14_3_up_boot(150605).bin), click Upgrade and wait for the process to complete. During the update, do not disconnect the power supply from the device, otherwise the device may be damaged.
After updating the firmware, the router settings could be reset to the factory settings!