I can not update to iOS 14 on my iPad

The original iPad Air, released by Apple in 2013, cannot be updated beyond iOS 12.X.

Hello ~ As *sberman* indicated you need a newer device. Go to upper black line and click on iPad 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~

You must purchase a newer iPad to use an iOS version greater than iOS 12.X.

iOS 12 is a older version. Your iPad may not be able to support or be compatible with iPad OS 14.