How do I upgrade the firmware on the TL-WA850RE?

Download the latest firmware file from www.tp-link.com, then log into the web management page at http://tplinkrepeater.net and go to Settings > System Tools > Firmware Upgrade. Click Browse to locate the downloaded firmware file, click Upgrade, and wait a few minutes for the upgrade and reboot to complete. Do NOT power off the extender during the firmware upgrade process, and ensure the firmware version matches your hardware version.