How do I update my iPhone 6 Plus to iOS 13.4.

Hello hellen162,

We have a great support article that might help with understanding updates. Please take a look at it here: Update your iPhone or iPad - Apple Support. That said, your iPhone 6 Plus cannot support iOS 13 or later. The last iOS update for the device is iOS 12.5.7. The iPhone 6S and iPhone 6S Plus can run iOS 15, but your iPhone is not able to.

We hope this helps. Let us know if we can assist with anything else at all. Take care.

Unfortunately, that is not possible. The iPhone 6 Plus can be updated to iOS 12.5.7, no further.