For the test, I will update the TP-Link TL-WR941N 300Mb/s V2 router with firmware 3.12.5 Build 100929 Rel.57776n.
1) Let’s look at the revision of the router, in my case it is V2, and just for it we download the archive with the new firmware from the official site, the first link for the 300Mb/c model, and the second for 450Mb/c.
https://www.tp-link.com/ru/download/TL-WR941ND.html
https://www.tp-link.com/ru/download/TL-WR941ND-450M.html
In my case, the latest firmware for V2 was 3.13.11 (121224) RU. If the firmware is not downloaded from the same revision, you can damage the router. Extract the firmware file from the downloaded archive.
2) Open the router settings by typing the address http://192.168.0.1 in the browser and enter the username and password, the default is admin/admin.
3) In the menu, select “System Tools” – “Firmware Update”, click the “Browse …” button and select the firmware file that was previously unpacked from the archive. Next, click the “Update” button and wait until the firmware is loaded into the router and it will reboot.
At the time of the update, you can not turn off the power of the router.
After updating the firmware, the settings in the router were reset to factory defaults, that is, you may have to configure it after updating the firmware.