Hi Christopher and welcome to the Disney Parks Moms Panel.
You can indeed upgrade your 6-Day tickets to Annual Passes so long as it is within 14 days of your 6-Day ticket’s first use and the ticket has remaining admissions.
Ticket upgrades must be made in person at the following locations at Walt Disney World Resort:-
•Theme park ticket windows
•Guest Relations locations
•Lobby Concierge at Disney Resort hotels
According to an answer provided by my fellow Moms Panelist Jennifer (which you can see
HERE), you will not lose any features of your Magic Your Way Package including the Disney Dining Plan when upgrading your 6-Day tickets to Annual Passes.
Last year, she upgraded a 3-Day Park Hopper ticket to an Annual Pass while visiting the Walt Disney World Resort on a Magic Your Way Package which included the Disney Dining Plan and encountered no problems at all.
Wishing you a magical trip filled with memories which will last a lifetime!
Emma