My Lightweight APs 1242 version is 12.3(7)JX. I am going to upgrade them to 12.3(11)JX. How can I do it?
Sorry, I guess I misunderstood your question. When a Lightweight AP is connected to the WLC it has the same Version as the WLC. For example if the WLC is running 184.108.40.206 the AP is running 220.127.116.11. If you upgrade the WLC to a new version the AP's are upgraded at the same time. There is no need to do anything with the recovery image.
Hope this helps!