how do i update my iphone 6

• If you have an iPhone 5S or 6/6plus, the highest you can update to is 12.5.5

• If you have an iPhone 6S through 13, you can update to 15.3.1

Go to Settings > General > Software Update.

Update your iPhone, iPad, or iPod touch using WiFi -

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

Update using your computer -

https://support.apple.com/guide/iphone/update-ios-iph3e504502/ios

iPhone 6 the latest updates was iOS 12.5.5 and those aren’t longer compatible with iOS 13.,14 and iOS 15