How do I change my current ticket to another showtime that is on the same day as my confirmation from the theater?

Unfortunately you will have to go in person to get it changed. As they will have to revoke the old ticket and issue a new one.

You will need to go to the theater box office to swap your tickets.make sure you have your current ticket or the card you used to make the purchase and they can look up your tickets from your card. You will need to go before the box office before the start of th show time that is earliest. If you want to go to a later showtime you will need to go before the current ticket show time. Once the movie has started for your current ticket you will be unable to change your ticket.