How to update 13 ios version?

It depends on your iPhone model. See this list for compatibility:

There is no iPhone in the world anymore that can run iOS 13, unless it had iOS 13 before iOS 14 was released and it was never updated.

I suspect you have an iPhone 6 or earlier; it cannot be updated past 12.5.4, as ProustGuilio’s response shows.

If you need a version higher than your hardware supports you will have to get a newer phone.

My phone is don’t update plz help i need 13 version