Recently, iOS 8.4 was released, and along with it, the Apple Music service was launched. However, if you have any problems
Save your iPhone data
Before doing anything to your phone, we recommend making a backup of iOS using iTunes.
By backing up your iPhone, you protectyourself from any failures that may occur during the iOS 8.4 downgrade process. If anything happens, you can safely restore your device from a backup and try downgrading iOS 8.4 again.
Downgrade to iOS 8.3
The first thing to do is checkiOS 8.3 signing status (there should be a green checkmark) on this website and download the iOS 8.3 file for a specific iOS device. The firmware files can be several gigabytes in size, so this will take some time.
Once the IPSW file for iOS 8.3 is downloaded to your computer, the next step is to open iTunes and connect your iPhone or iPad to your computer.
Then go to your device's review page in iTunes and hold down the Option/Alt key on your keyboard (or Shift on Windows) and clickRestore iPhoneon iTunes.
This will open the file manager window, and you will be asked to select the firmware file. Select the file you downloaded earlier.
Your iPhone will begin restoring back to iOS 8.3. This process may take several minutes.
Once the iOS 8.4 downgrade process is completed, you will have a clean iPhone running iOS 8.3, if you want, you can restore all your apps and settings. Go back to iTunes and clickRestore from copy.