Hi Tracey,
You can absolutely upgrade your FREE Quick-Service Dining Plan to the regular Disney Dining Plan and simply pay the difference. My family will also be staying at Port Orleans Resort in October and have done just this.
You can find out more information on both of these Dining Plans by downloading the PDF brochures
HERE.
If you decide that this is something which you would like to do, you will need to contact the company with whom you made your original holiday package reservation with. They will be able to tell you what the exact cost of upgrading your Dining Plan will be will be.
It is well worth the extra money in my opinion and there are so many fabulous table-service restaurants at Walt Disney World to experience.
If you do upgrade, I would strongly recommend that you make advance dining reservations for your table-service meals straight away. As advance dining reservations can be made up to 180 days in advance, and you are travelling during a time when FREE Dining is being offered, I suspect that many of the popular restaurants will be booked up already.
Dining resevations can be made online at the Walt Disney World website
HERE.
Wishing you a magical holiday!