There is another way without itunes Restore:
1- Make sure your iPhone is at latest iOS
2- Backup your iPhone (Preferred on Cloud)
3- from you iPhone go to: settings - general - reset - reset all media and settings - WILL PERMANENTLY DELETE everything from your iPhone.
4- Connect your iPhone to iTunes - it will tell you "Congratulations .. you iPhone is unlocked"
5- Setup your iPhone by restoring your backup (preferred from cloud as in #2).
it will take you time to restore your iPhone but it is easier than restoring through iTunes