How can I update to iOS 10 my generation 2 iPad

Expanding upon lobsterghost1’s comments...

iPad2 cannot be updated beyond iOS 9.3.5 (WiFi Only models) or iOS 9.3.6 (WiFi & Cellular). Apple ended update support for iPad2, iPad3 and mini1 in September 2016. None of these models can be updated to iOS 10 or later versions, as the internal hardware does not meet the minimum technical requirements for new versions of iOS/iPadOS. The 32-bit platform upon which they are built is effectively obsolete.

Many App Developers have also dropped support for older devices and iOS versions preceding iOS11/12/13 - and have withdrawn older versions of their Apps from the Apple App Store, now limiting utility and usefulness of older devices. 

If Apps that you need to use now have higher minimum iOS-version requirements, your only option is to replace your iPad with newer model. Of current models, even the entry-level iPad7 model supports current iPadOS 13.x and soon to be released iPadOS14 - and has hardware specifications and capabilities that will vastly outperform your old iPad.

I hope this information is helpful - if only in clearly stating the limitations of your current iPad and your potential options.

You can't, sorry. iPad 2 is now a 9 year old, too under powered, no longer supported, completely incapable of running anything beyond iOS 9.3.x device.

It is now well past it's prime 9 years later and if you need higher iOS levels, you will have to replace your iPad with a more modern iPad capable of running the newest iOS levels. iPadOS 14 will be out soon, that's how far behind your iPad is.