Can I change it to IOS 13.1

An iPhone 6 can't be updated beyond 12.5.7, it doesn't have the hardware needed to run anything higher.

If you need a higher iOS version, you will have to purchase a newer phone.

To update to 12.5.7 _

Go to Settings > General > Software Update.

This link will show you how to update your iPhone, iPad, or iPod touch using WiFi -

Update your iPhone or iPad - Apple Support

This link will show you how to update using your computer -

Update iOS on iPhone - Apple Support

ohobu Said:

"Can I change it to IOS 13.1: how can I change my iOS 12 too iOS 13.1"

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Installing iOS13.1:

No. iOS13.1 is no longer an option for updating, whatever the model. Only the latest, compatible version would install.

If you're referring to an iPhone 5s, 6, or 6 Plus, it's not capable of 13 or above. Otherwise, use a computer or the Software Update function in Settings to install 15.7.3 or 16.3.

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