How to update 13 ios version?

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.

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

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