Start with the IOS image, ap3g2-k9w7-tar.152-4.JB5.tar. Then the Release notes: OL-31714-02 (1) Which says your are out of luck, unless you ONLY want to do Site Survey's with the 3702!
The RN's do also explain how to accomplish the downgrade.(oops wrong, just which ios does what)
If it is linked to the WLC then you can cli the following:
config ap tftp-downgrade tftp-server-address filename access-point-name i.e.:
config ap tftp-downgrade 192.168.1.10 ap3g2-k9w7-tar.152-4.JB5.tar Survey
You might also find Rasika's guidance to your liking for the manual method:
http://mrncciew.com/2012/10/20/lightweight-to-autonomous-conversion/
