How to update my iPhone 6 Plus

The links below should provide the requested instructions to upGrade the iPhone

Just be sure to have enough Empty Space on the iPhone to allow the upGraded to download, expand and then install

Update your iPhone or iPad

How to check the storage on your iPhone and iPad - Apple Support (CA)

iOS 12 is compatible with these devices - Apple Support (CA)

iOS 13 and iPadOS are compatible with these devices - Apple Support (CA)

iOS 14 and iPadOS are compatible with these devices - Apple Support (CA)

iOS 15 and iPadOS 15 are compatible with these devices - Apple Support (CA)

Follow on and if a previous Contributor assessment if accurate

All it not lost

If the user wishes to explore the Apple Trading In option where the Value of the exiting machine could be used against the cost of a new Apple iPhone.

Have used both previously and have been satisfied each time.

The iPhone 6Plus cannot be upgraded further then iOS 12.5.6 due to hardware limitations