how to update?

Hello,

The 5s only supports up to 12.5.1. See this:

https://discussions.apple.com/thread/252542374

Good luck.

I am Sorry to say that only iPhone 6S and above can update to iOS 13. Therefore, your iPhone 5S cannot be updated beyond iOS 12.

If you are facing performance issues, you could:

Have the battery Replaced.

or

Trade in your iPhone for a new One.

your iphone can just update to ios 12