Don't want the latest software or the firmware rather want to use old one? Then here is what you can do to downgrade your iOS version with any device.
Step 1: Download old version of iTunes (11.0.5 or earlier) and install it but before that if you already have then remove that completely.
Step 2: After that download iOS firmware the one that you want to downgrade your device to which is compitable with your device from http://ipswdownloader.com
Step 3: Now keep on pressing Home button and power button at the same time in your device. After a while your device will restart and iTunes logo will appear with a picture of USB cable indicating that your device is in recovery mode. Let go of the button.
Step 4: Connect your device to the computer and open iTunes, on opening iTunes a pop-up windows will appear asking you to restore your device. Don't click ok just close that and press shift in windows and Alt/option key in Mac and click restore.
Step 5: A window will appear after clicking on restore, from that window locate the location of your downloaded firmware and open it.
Step 6: Now you are good to go. Everything will be done just have same patient.
NOTE: Anyone trying these steps please be aware that sometimes because of some problem your device may not be downgraded and I am not responsible for any of the copyright claim or other stuffs that you carry out. Not only in these post it's same with the previous one and upcoming too...
If anyone of you have any problem do inform me I will be happy to help.