Update my iPhone

Update your iPhone, iPad, or iPod touch

• If you have an iPhone 5S or 6/6plus, the highest you can update to is 12.5.7

• If you have an iPhone 6S through 7, you can update to 15.7.3

• If you have an iPhone 8 or higher, you can update to 16.3.1

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 Update your iPhone or iPad - Apple Support

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

Update iOS on iPhone - Apple Support Update iOS on iPhone - Apple Support

Assuming that you have an iPhone 5s, iPhone 6 or iPhone 6 Plus......You can update to iOS 12.5.7

Good Wi-Fi signal

Fully charged battery

Free space of 6 GB or more on the phone

Settings > General > Software Update