How do I update my iPad to iOS 11?

I suspect you have the iPad 4th generation from 2012, as that model supports 10.3.3 (10.3.4 for cellular) but not iOS 11, 12 or 13 as the hardware of that device is too old for anything newer.

If you want or need iOS / iPadOS 13, you would need to buy a new iPad.

www.apple.com/ipad

If you're on 10.3.3, your iPad cannot be updated further. You need a newer device.

~Lyssa