How to reset old APs and upgrade them to the latest firmware.
power up
hold reset for 10 seconds
use the chrome unifi app to get IP address
use PuTTy to ssh into the AP using ubnt for the username and password
run this command to upgrade the AP
upgrade http://teacher.nicholas.kyschools.us/tech/downloads/BZ.ar7240.v4.3.20.11298.200704.0747.bin
should then be able to adopt the AP in the controller.