How to upgrade my iPhone 5s?

Hello ~ You can update to 12.5.8 I believe. What happens whe you try? Take a look here in the meantime:

Update your iPhone, iPad, or iPod touch - Apple Support

~Katana-San~

iPhone 5 is an outdated iPhone, can’t be update to a higher iOS.

iOS 10.3.4 is the latest iOS version for iPhone 5

iPhone 5S is an outdated iPhone, can’t be update to a higher iOS.

iOS 12.5.5 is the latest iOS security update -> released September 23.

If you have an iPhone 5, then the highest iOS version that can be installed on it is iOS version 10. Nothing further.

If you have an iPhone 5s, then the highest iOS version that can be installed on it is iOS version 12. Nothing further.

Which of the two iPhone models do you have? To check, open Settings ➔ General ➔ About.

Review the instructions in this guide published by Apple to learn how to ➔ Update your iPhone, iPad, or iPod touch - Apple Support

Axel F.