How to downgrade your iPhone or iPad from iOS 9 to iOS 8.4.1
Note that downgrading devices to iOS 8.4.1 will only work for as long as Apple continues to allow for this to happen by signing the firmware files for this iOS version. Also, before moving on to downgrading your device from iOS 9, make sure to create a backup of your personal data, as as the procedure we're about to explain will wipe your device clean.
While downgrading from iOS 9 to iOS 8.4.1 may seem like a daunting task, you need not worry. This article will provide a detailed step-by-step guide through the entire process:
Step 0: Go to the following link and download the iOS 8.4 ISPW file for your device on a computer with iTunes.
Step 1: Go to the Settings app on your iPhone, then turn off the Find My iPhone feature. If you're downgrading an iPad, don't worry about this.
Step 2: Hold the power button then do a swipe to turn off your device.
Step 3: Go to your computer and launch iTunes.
Step 4: Right after you connect your iPhone or iPad to his computer, start holding both the power and the home button for about 10 seconds. Then release the power button, but continue holding the home button for about three seconds. Use a clock to time the moves.
Step 5: If you've timed everything correctly, iTunes should now detect that your iPhone or iPad is in device firmware update mode. If the device boots up normally, repeat steps 2 through 4 again.
Step 6: In iTunes, select the device and go to the Summary screen.
Step 7: Press the Restore button while holding down Shift (Windows) or Option (Mac).
Step 8: When the file browser opens, navigate to where you've downloaded the iOS 8.4.1 IPSW file that you've previously downloaded.
Step 9: Once the setup routine is complete, your iPhone or iPad will go to the new setup screen, just like a new device would.