If you're going to get a new DL AMEX card, definitely APPLY for it. Don't upgrade your existing AMEX card.
To qualify for whatever bonus offers are available including bonus Skymiles, you must Apply.
Go to the American Express website to see the ever-changing offers.
You might get enough bonus Skymiles to get that second free ticket.
Upgrade will get you nothing.
You can then cancel your existing card if you feel you no longer need it.