How can I tell if firmware has been updated

I've just used 540 MB of my data allowance despite telling my Note 2 to only download firmware update using wifi. No drama cos it's within my allowance. But how do I finish the process? Settings shows Android 4.1.1 so I assume not updated. But data usage shows 540 mb by android os

You don't say who your supplier is but Verizon does not charge the update against your data limit. If you go to menu>setting>about phone it will show your OS version