The firmware update procedure of Linksys re6400 setup entails updating the extender's operating software to the most recent version. Make sure your computer is linked to the same network as your extender and that it is connected to a reliable power supply before you start. Open a web browser and type the default IP address (often 192.168.1.1) in the address bar to reach the Linksys web-based configuration page. Go to the "Administration" or "Firmware Upgrade" option after logging in. Save the most recent firmware to your computer by downloading it from the official Linksys website. The firmware update can then be started by selecting the downloaded file by clicking "Upgrade" after clicking the "Choose File" or "Browse" button in the firmware upgrade section. Meanwhile, don’t turn off the PC and the extender to avoid interruption or damage to the network further.