If you are NOT trying to change it to a specific channel, but bump it to a random channel, you must wait 8 minutes (the default ARM holdown timer) until it even considers changing channel. An access point saves its last channel in flash, so if it was to be powered off, that is the channel it will come back up on.
If you ARE trying to change it to a specific channel, you need to save a copy of the default regulatory domain profile, name it something different, and remove all of the allowed channels that you don't want the access point to be on. Next, you would need to go into the AP specific profile for that AP and Apply that new regulatory domain to the AP.