None of the legacy/network airlines allow traveler changes AFAIK.

If it's a refundable ticket, refund it and buy one for the new traveler (or have him/her buy it.)

If it's non-refundable, you can cancel it and use the value of it within one year of ticketing, for the same passenger only, with payment of the fare difference and the change fee (typically $150 domestic/250 international).

If it's an award ticket, you can redeposit the miles for a fee (unless you're Platinum where I believe it's waived) and book a new ticket with miles for the intended traveler.

But never possible to assign the ticket to a different passenger.