I finally managed to update my iPhone 4s via iTunes. I downloaded the update on my Mac laptop ( the ipsw file from ipswdownload.com ). I connected my iPhone to the laptop via usb. After iTunes recognized the iPhone and showed the check for Updates Button. I clicked the check for updates button while holding the option button. That will bring up the ability to choose and open a file. Choose the correct ipsw file for your particular device that you just downloaded ( there are different ipsw files for each device so make sure you download the correct file ). After selecting the correct ipsw file hit the open button followed by the update button. It may look like the installation has stalled with the waiting for iPhone ( iPad ) showing in iTunes for a very long time before anything starts to happen. It seems to take forever to complete the installation. My install took 20 minutes so don’t quit iTunes thinking it’s stalled or you’ll be left with a device showing the connect to iTunes graphic and have to repeat the whole process all over again. This worked for me so hopefully it will work for you. On my iPhone after the update downloaded and the iPhone restarted I got a screen saying to update slide here. You slide the button and you get another install screen similar to when iTunes is updating your iPhone ( not sure if it will be the same on an iPad ). After the progress bar completes my iPhone restarted in iOS 9.3.6
Aah, would have liked to add to my previous comment, but tampered with the wrong keys, I presume Would just like to say magic happened. On my phone screen popped invite to update, and with not much hope I followed through – and it processed along, just like in the old days!And yeah, I've got kind of an idea of firmware now, could have looked it up myself on beforehand.