The data of already purchased e-tickets cannot be changed. You have to purchase a new one and to return the origin one accordingly to the Terms and conditions of usage of the e-ticket (listed in the text below the e-ticket´s itinerary in the PDF file) and accordingly to the Terms of the Carrier and accordingly to the Terms listed on the e-tickets itinerary (returning’s charge / time limit before the departure of the connection in hours till which the ticket is still returnable with the corresponding charge).