Question about adding to park tickets - locations?

[Mambo Junkie]

I know you can add a day at guest services at the parks and Disney Springs. Are you able to do it at the resort? Also, we have 5 day tickets - we can add a day anytime before the last day is used, correct? (and still get the same Price). Is there anywhere else that guest services may be? I'm just trying to avoid using park time to upgrade.