how do I update my ipad2 ios4.3.5 to ios9

how do I update ipad 2 ios 4.3.5 to ios 9

First, make sure you have your device backed up so if you run into issues your data will be protected.

Then, you need to connect your iPad to iTunes on a computer, and update it from there. I believe it should let you update to the highest iOS for that device.