This should be interesting. I sent RD an email about where to report for upgrading and they replied "Unfortunately, we cannot answer that question here at runDisney. Please check out the Disneyworld.com site for more information."
LOL, oh well.
Turns out, we need our tickets to enter the parks Thursday anyway so I'm thinking I won't be able to upgrade. I'm guessing they will take your unused tickets, not bridge them but apply what you paid towards the cost of an AP. I think someone already mentioned that, but I'm doubting they'll bridge used RD tix. But I don't know what I'm talking about so there's that.