There are differences in what you will owe, based on where you purchased your tickets. If you bought direct from Disney, either online (not connected to a resort stay package) or at a WDW ticketing outlet or Guest Relations, you would owe the difference between what you paid for your original ticket, and the current cost of the upgraded ticket.
Another category of acquiring a ticket involves purchasing Disney tickets, but not directly. This group includes Disney resort package tickets, tickets purchased at the
Disney Store, and tickets purchased from authorized third party resellers (such as Tickets At Work). Tickets from these venues can be "price-bridged." That means that the ticket will be given credit for the current day's gate price, regardless of any discount given or any price increases in-between original ticket purchase and upgrade to new ticket. What you paid for your ticket won't come into play. The way you do a price-bridge is to simply use your original ticket to enter a theme park. (You won't get gate price credit if you upgrade before actually using your original ticket.) Once your original ticket has been used, take it to Park Guest Relations for your upgrade. Don't try to do this at your resort. You don't have to do it immediately - only have to do it before the last park day of your ticket is used and done with. A few ticketing personnel don't thoroughly know the price bridging procedure. If you encounter a CM who tells you an amount that is too high, ask if they gave you gate price for your ticket. If they won't change their calculation, find another CM to help you.
Current gate price (including tax) of your 5-day MYW ticket is $323.76.
Current gate price (including tax) of regular AP is $675.21.
Difference you will pay is $351.45.
There could be a price increase between now and November. However, if you follow instructions above, you will still be paying the gate price difference between the two tickets.