1. Install and open itunes
2. Hold down the Iphone’s home button then connect it to to your computer until you see the recovery logo as seen below then release the home button.
3. click Restore as seen below to restore the device files then click Update.
4. Wait itunes to download and install IPSW File on ypour iphone.
Method 2:
1. Download the appropriate IPSW File for your iphone from here or here or here.
2. Open itunes and hold down the Shift key and click restore to browse to your desktop and select the custom IPSW which you downloaded.
3. Now, wait while itunes restores the custom IPSW on your iphone. Once restored, your it will reboot automatically.
