I bought the 3-day park hopper from Costco. I am thinking I may want to take the kids to the parks one last time on the day we check out as our flight doesn't leave until after 6 - and we are going during Spring Break - and we are staying onsite - sooooooo one more early entry 
So my question is - can I upgrade my Costco ticket when I am there to add another day or will I need to pay for a seperate single day ticket? If I can upgrade, how do I go about doing that?
Thanks for your help!

So my question is - can I upgrade my Costco ticket when I am there to add another day or will I need to pay for a seperate single day ticket? If I can upgrade, how do I go about doing that?
Thanks for your help!