How can I update iPad2 of iOS 9.3.9

Hello~ You can’t update your iPad higher than iOS 9.3.6. If you need a higher version of iOS…you will need a newer device. To shop for a new iPad click on below…

iPad - Apple Official Site

Also…Take a look here if shopping for a second hand device to make a more informed decision.

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~

An iPad 2, iPad 3, or iPad mini 1 isn't capable of 10 or above; they require an A6 or better CPU. There isn't a 9.3.9.

(257516)

you can use the apps installed and you can use apps from app store which does not require a newer ios than the iPad support and the is pretty much it