aktualizacja systemu

Check -> iPhone type & iOS version -> Go to Settings -> General -> About.

iOS 12.5.5 is last security updates for iPhone 5S.

What happens when you go to Settings -> General -> Software Update?

How to update the system if iTunes version 8 does not read iPhone.

See -> If your computer doesn’t recognise your iPhone, iPad or iPod

If your computer doesn’t recognise your iPhone, iPad or iPod – Apple Support (UK)

See the following Apple articles:

Update your iPhone, iPad, or iPod touch

Update your iPhone, iPad, or iPod touch - Apple Support (IN)

If your iPhone, iPad or iPod touch won’t update

If your iPhone, iPad, or iPod touch won't update - Apple Support 

You can do the update via PC, see this Apple article: Update software on iPhone, iPad or iPod touch in iTunes on PC

Update software on iPhone, iPad or iPod touch in iTunes on PC – Apple Support (UK)

If you have a Mac see this Apple article: Update your iPhone, iPad, or iPod touch with the Finder

Update your iPhone, iPad, or iPod touch with the Finder - Apple Support

You need about 4 - 5 GB device storage and good Service & Wi-Fi.

If they are On, turn Off Hotspot & VPN.