When using the console, stop the AP at the apboot> prompt and then type "purge" and press enter. Type "save" and then press enter. That should purge the AP.
You can also set the AP parameters manually by using the "setenv" command:
setenv ipaddr <ip address>
setenv netmask <subnet mask>
setenv gatewayip <default gateway>
You also need to point the AP to the address of the master controller:
setenv master <master controller ip address>
After that type "save" and then "boot"
To see what parameters you have, type "printenv"