How can I update the iOS?

• If you have an iPhone 5S or 6/6plus, the highest you can update to is 12.5.4

• If you have an iPhone 6S or newer, you can update to 14.7.1

Update your iPhone, iPad, or iPod touch -

https://support.apple.com/en-us/HT204204

Andino13 Said:

"How can I update the iOS?"

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Use a Computer:

You can do so using a computer. Learn how to here: Update your iPhone Using a Computer - User Tip

Click on the blue text in the response you got. It is instructions on how to update your device.