I am using Samsung Galaxy A7. Today I encrypted my device and secured it with a password lock. Now I need to permanently decrypt the device but I cant. When I go to settings and try encrypt option there is no option to deactivate it.
The only way to remove encryption on a previously encrypted Android device is to perform a full factory reset. This means wiping out everything, including contents of the /sdcard partition and losing all your media, so make sure to perform a back up first.
Keep in mind that some Android 5.1 devices enforce full device encryption by default. On these devices even factory reset will not remove encryption, as the device will re-encrypt itself upon first boot-up. The only way to override this is with a custom kernel.