iPhone users have the option to set a four-digit security password when powering or unlocking their phones. If the wrong password is entered too many times, however, the phone will disable itself, allowing no one to unlock it --- even when the correct password is entered. In order to access the iPhone again, the user must reset the password by restoring the phone from a backup using iTunes.
Open iTunes on your computer. Make sure your iTunes software is the most recent version. If not, click "Update" to get the newest software.
Plug your iPhone into the computer using the USB cable.
Click on your iPhone under "Devices" in the sidebar on the left side of the screen.
Select the "Summary" tab at the top of the screen. This will display your iPhone's information.
Click "Restore." A window will open asking if you wish to back up your iPhone. If you have recently backed up or synced your iPhone, this is not necessary. Otherwise, click "Back Up." This will save all the data stored on your iPhone.
Select "Restore" in the next window. This will reset your iPhone to its original settings.
Click "OK" after your iPhone has been reset to factory settings. The "Connect to iTunes" screen (an image of a USB plug pointing to the iTunes logo) will appear on your phone. Leave your phone plugged into your computer.
Select the backup date you wish to restore your iPhone to and click "Continue." This will transfer all the information back on to your iPhone, allowing you to access it without a four-digit password.