Flash like most ubiquiti devices:

Download this image:

http://downloads.openwrt.org/backfire/10.03.1-rc4/atheros/openwrt-atheros-ubnt5-squashfs.bin

Push the reset button and then plug the power to the device keeping the button pushed. The leds will start blinking red and yellow, you can now release the reset button.

Now you can tftp the image to 192.168.1.20