https://help.ui.com/hc/en-us/articles/204977444-airFiber-Updating-the-Firmware

Quick list of commands

ssh ubnt@192.168.1.20  <- Replace with username and IP address
cd /tmp
wget http://dl.ui.com/firmwares/airfiber11X/v4.1.0/AF11.v4.1.0.bin
mv AF11.v4.1.0.bin fwupdate.bin
/sbin/fwupdate -m

1. Upload the firmware using FTP or SCP to the /tmp directory
2. Rename the file from AF11…bin to fwupdate.bin
3. Start the upgrade with

/sbin/fwupdate -m

Wait for it to finish upgrading