I want to update my iphone6

Hello ~ Your iPhone 6 can only be updated to iOS 12.5.6. Most apps need a higher version of iOS to be used so you need a newer iPhone. Go to upper left click on 2 lines and then iPhone to see your new choices. If you consider a second hand device please take a moment to read these…

Activation Lock for iPhone, iPad, and iPod touch - Apple Support

Also:

The All Too Common SAD Reality of Buying a Used iPad/iPhone

~Katana-San~

Your iPhone is too old and would not be compatible with the newer software updates.

The time has come:

Shop one-on-one with a Specialist at an Apple Store.

Click ▶︎ Reserve a Shopping Session. 🛒