How do I restore iPad and install the latest version of iOS?

You don’t have to restore it to update the the newest version, however, keep in mind, the hardware is going to have to support the newest version of OS, but you can get the latest version of whatever version your iPad will allow by going to Settings>General>Software Update and will tell you what the latest version is that you can install. If you want to restore first you go to Settings>General>Reset>Erase all Content and Settings.

Saying this, if you don’t have the most current version and you can’t support the most current version if you restore it, it you could make the iPad unusable as you will remove everything that is on it, and you may not be able to get the apps back on the iPad because it will try to get the newest version of that app and won’t let you because you don’t have the most recent version of iOS and you won’t be able to get the most recent because your iPad won’t support it. So make sure that you can support it before you go this route.