Where to upgrade my MYW ticket *before* checking in to resort?

[pjynx]

We purchased MYW tickets but when the AP rates came out, we booked our room using an AP rate. I know I need to upgrade one of our tickets to an AP before we check in so they will honor the discounted rate. Where would be the easiest place to upgrade my ticket? We're staying at FW cabins, so MK would probably be closest, but considering that we'd have to park and then take WDW transportation from the parking lot to the gate, that doesn't seem very easy (esp since we've never been here before and will probably not have a clue what we're doing, LOL). Would any other parks be easier to access the gate from the parking lot? Any way we can avoid paying to park (since we are staying on property, but we won't have our resort ID's yet). I think I've also read something about a guest services bldg in downtown disney? Would that be an option?

Thanks!