The best thing you can do is restore the iPad and put a "fresh" iOS 5.1.1 on it. That way, all the old data is erased - because you are putting it back to a "fresh, out-of-the-box" state when you restore it.
So, my recommendation is to connect the iPad1 to your iTunes and press the "Restore" button. iTunes will do its magic and, when its done, you'll have a clean iPad1, ready for you.
Marilyn