You can't do it in Settings. Your Apple ID password can be changed by signing into your account in iTunes on your computer or in the iTunes app on your iPad. If you're doing it on your iPad, scroll to the bottom of the iTunes store page and tap on your Apple ID button. in the pop up that appears, tap on View Apple ID. At the top of the next page, tap on Apple ID. You'll have to sign in and answer your security questions. On the next page, tap on Security. On the next page Tap on Change Password and follow the instructions to change your Apple ID password. Once changed. your new password will work on every device associated with your Apple ID.
Just a reminder that you need an active internet connection while changing your password as you'll be connected to Apple servers when doing so.