used iPhone4s upgrade to ios 7

[elgenon]

I bought a used iPhone 4S 16G and want to install the Uber app. It says I have to have at least ios7. I want to do the minimum upgrade possible as I heard they slow the phone. I recently downloaded an update for iTunes on my laptop.

Assume I no nothing (which is true) and please tell me step by step how to upgrade and if I can upgrade to 7 and not 8.

Thanks!

[DrWats0n]

Apple stopped signing iOS7 long ago. Usually after an iOS update release, the previous iOS version is supported for a little while and then the signing stops meaning you can no longer install it.

I believe you'd have to go to iOS8.4.

[elgenon]

I read a post where an owner of an iPhone4 regretted going to 8. So I need to forget Uber or get a new phone?

I was hoping to use Uber on my next trip to Suvarnabhumi.

Any ideas?