Hi Haley!
Welcome to planDisney! Thank you so much for sending this great Disneyland Resort Theme Park Planning question to us hEAR!
I'm happy to say that yes, you can upgrade your
Theme Park Admission Ticket from a single-park-per-day to the
fun-derful Park Hopper option midway through your Disney day! To do this you'll need to visit the ticket booths in The Esplanade area between
Disneyland Park and
Disney California Adventure Park as at this time there isn't a way to make this upgrade in the
Disneyland Mobile App. I've actually done this before with both standard tickets as well as tickets purchased through a
promotional offer.There are a few important things to note, though. The first is that if you have a multi-day ticket, upgrading to a park hopper today will also upgrade the rest of the days left on said ticket. Secondly, there is no pro-rated price if you choose to upgrade to a hopper later in the day, so be sure to make this change as soon as possible so you don't miss out on all of the park hopping fun which starts at 1:00 P.M. PST. Lastly, your
Disney+ add-on will be retained for the day; there's no need to purchase that again.
I hope that this helped to up the fun factor on your Disney Day! Thank you again for reaching out, and if you have any more Disneyland Resort questions, Haley, We're All Ears!
~Kristen