I phone 4 s iOS update

If you're sure that your iPhone is a model "4s" (not a model "4"), you should be able to update it to version 9.3.6.

On the contrary, if it is a model 4, iOS supported version can't go beyond 7.1.2.

See also this guide:--> Update your iPhone, iPad, or iPod touch - Apple Support

Regards

Giulio

Update the iOS software on your iPhone, iPad, or iPod touch - https://support.apple.com/HT204204 - When you update you will only be given one update selection which will be the highest available iOS version supported by your device. If it says no update is available and you need a higher version you will have to buy newer equipment.

For a 4S this will be 9.3.6 which was released recently.

Update your iPhone or iPad software to avoid issues with location, date, and time - https://support.apple.com/en-us/HT210239

"Starting November 3, 2019, some iPhone and iPad models introduced in 2012 and earlier will require an iOS update to maintain accurate GPS location and keep the correct date and time. This is due to the GPS time rollover issue that began affecting GPS-enabled products from other manufacturers on April 6, 2019. Affected Apple devices are not impacted until November 3, 2019."

If you want to update to 9.3.6 on an iPhone 4S you can try doing this over wi-fi but I have tried several times and it gets hung up on the "downloading" message, If you try with iTunes it will have to be on a computer running El Capitan or newer and iTunes 12.8 (I tried with an older computer with iTunes 12.6.1 and it told me I had to update in order to install the newer iOS so I'll go to an Apple Store to do it).

Uh, I think the OP clearly stated it was a 4S. Not sure what was wrong with my post that Apple didn't like it since it already said what was said in later posts anyway. Link to how to update and max. iOS for a 4S. ?? Clearly there is something wrong with the information in it and later posts which duplicate the information so anybody reading this later beware that there is some error in there I am not seeing and don't follow its advice or similar advice without calling Apple first to verify the information.

Contact Apple for support and service - "See a list of Apple phone numbers around the world." - https://support.apple.com/HT201232