If you attempt to use Disneyland (California) tickets at Walt Disney World (Florida), the tickets will not work at the gate. Although both are owned by the same company, they operate as separate business entities with entirely different ticketing systems and pricing structures. You cannot "convert" or "transfer" a Disneyland ticket directly to a Disney World ticket at the ticket booth. However, Disney is known for its "Guest Excellence," and while they aren't obligated to help, you can visit a Guest Relations window. In some cases, if the tickets are unused and unexpired, they may be able to provide a credit for the amount paid toward the purchase of new Disney World tickets, but you will still have to pay the difference. To avoid a major headache, always double-check your destination before clicking "purchase" on the Disney website.