Hey there, Myriam! Thanks for visiting us at planDisney. You must be very excited for upcoming visit.
Myriam, ticket upgrades are possible but subject to availability. With a
Park Hopper ticket, you are selecting the park where you’d like to start your day, when you make a reservation. Hence, the availability for
One Park Per Day or Park Hopper tickets may vary.
The cost to upgrade to a Park Hopper ticket is currently $60 per ticket (price subject to change.) Currently, the cost of adding the Park Hopper option is for the entire duration of your ticket.
My suggestion is to check with the Disneyland Resort Main Entrance Ticket Booth when you arrive to see if an upgrade is possible. If so, you will be able to pay the difference to upgrade.
Sending you a pinch of pixie dust for good luck! Wishing you a magical visit.
Kamini