I have some AP1242 and 1 WLC 4400.
Is it possible, I "downgrade" my AP for autonomous? If yes, wich IOS I use for this.
Yes. You can read about it at the link below (the process works regardless of whether an AP was originally lightweight or autonomous). Follow the steps very closely (especially step 1!):
Download the IOS image from the Cisco wireless downloads area. The most current version of IOS for the 1240 is c1240-k9w7-tar.124-21a.JA1.tar: