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. If you don't have shsh backup, please view this tutorial "How to Downgrade iPhone 4 from iOS7 to iOS6.1.3 without SHSH Blobs Using 3uTools?"
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 computer, and then download the latest version of 3uTools.
Step 2. Click Flash Jailbreak→Pro flash→Query SHSH. And then you can see which firmware versions you can flash your device to if you have backuped the SHSH files before.
Step 3. Download firmware. For example, you want to flash it to iOS6.0.1 now. Click "Firmware"→choose "iPhone 4"→click the downloading icon of “iOS6.0.1”.
Step 4. Click the icon on the upper right corner to enter Download center, and please wait till the download is completed.
Step 5. Click Completed→click the yellow icon of “search” to confirm the firmware location.
Step6. Click Flash Jailbreak→Pro flash→Select Firmware, and then pick up the firmware. Click Flash now to begin the flash.
Step7. Please wait till the flash is completed. When the iTunes sends a reminder in the flashing process, please cancel the box, or your device will be restored to the latest iOS version instead of 6.0.1 on iTunes!
* As to the feature of backuping SHSH file, it is involved in the toolbar of "Advanced" on 3uTools.
*3uTools will probably downgrade more devices later, but it can currently downgrade the following devices:
1. iPhone 3GS without SHSH file backup can be downgraded to iOS4.1 using 3uTools.
2. iPhone 4 with SHSH file backups can be downgraded to any compatible firmware using 3uTools.
3. iPhone 4s/5/5s/6/6Plus/6s/6sPlus, iPad 2/3/4, iPad Pro, iPad Air 1/2, iPod Touch5/6, and iPad mini 1/2/3/4 can be downgraded from the 9.3 to 9.2.1 using 3uTools.
*Tips for other devices:
1.iPhone 4s without SHSH file backup can be downgraded to iOS 6.1.3 using odysseus-0.4.
2.iPhone 5 with SHSH file backup can be downloaded to iOS7.0.4 using odysseus-0.4.
3. iPhone 5s can't be downgraded with whichever tool.