I've recently converted my autonomous AP (1252) to a LAP. It is now controlled by my 4402 WLC (version 4.2.112).
How can I change the password on the 1252? As I stupidly left it as the default before up I upgraded. I just used a tar file and the archive download-sw method.
That password you had initially when the ap was in autonomous does not matter. Now since you have the ap joined to a wlc you need to enter the following command in the wlc cli:
config ap username password all
config ap username password
All configurations on the AP will be done by the WLC. You can't configure the LAP like an autonomous ap.