3uTools can downgrade iPhone 4 from iOS7.1.2 to iOS 4.0-6.1.3 only in the case that you have backuped the particular SHSH files before.
Notes before flash:
1. Please use iTunes to backup your important data before flash.
2. Please directly connect your device to the computer via the USB cable, and don't use the extension cable or front USB.
3. Ensure you remember your iCloud account and password, or your device can't be activated after flash.
4. If the app immediately jumps to the main menu as you click the app icon after flash, please reinstall the app.
5. Check the box of “Don't erase user’s data” so that your phone data can be stored.
6. Steps to enter DFU mode: Keep the device in normal mode or recovery mode, plug in USB cable (please don't use USB extension cable); hold HOME button, then hold power button till the screen becomes blank; release the POWER button after about 4 seconds, but keep holding the HOME button for about 10 seconds.
Step 1. Ensure you have installed the iTunes on your comput
er, and then download the latest version of 3uTools.