How do I update my iPhone 6 to 13.0

You don't. The latest - and likely final - version of iOS for the iPhone 6 is 12.5.5. If you have apps, or want to use apps, which require a later version of iOS, then you have no option but to purchase a new phone. Some mobile service providers may still offer iPhone 11s if you don't want an iPhone 13. An iPhone 11 is capable of running the latest version of iOS (15.1).

An iPhone 6 isn't capable of 13 or above. Try downloading them to a newer unit on the same Apple ID first.

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