How to update iPhone 6 iOS?

iPhone 6, iOS 12

1.

iPhone 6 is an outdated iPhone, the last security updates iOS 12.5.6.

Go to Settings -> General -> Software Update -> Download and Install.

You need about 6 GB device storage and good Service & Wi-Fi.

If they are On, turn Off Hotspot & VPN.

Charge the battery > 70%.

See the following Apple articles:

Update your iPhone, iPad, or iPod touch

Update your iPhone, iPad, or iPod touch - Apple Support (IN)

If your iPhone, iPad or iPod touch won’t update

If your iPhone, iPad, or iPod touch won't update - Apple Support

You can do the update via PC, see this Apple article: Update software on iPhone, iPad or iPod touch in iTunes on PC

Update software on iPhone, iPad or iPod touch in iTunes on PC – Apple Support (UK)

If you have a Mac see this Apple article: Update your iPhone, iPad, or iPod touch with the Finder

Update your iPhone, iPad, or iPod touch with the Finder - Apple Support

2.

It is not possible to update your iPhone to a higher iOS (13 and later).

Yes, most apps require iOS 13 or later, such as Facebook & YouTube app requires iOS 13.4 or later.

Considering a newer type of iPhone?

Please read this before you buy a 'newer' type iPhone.