For domestic itenearies, you can try online (if it has a change flights button: for me it never even has it for domestic, only for a few int'l, and for those it never ever works), there it's a lower change that just searching for flights online it'll outright wipe out (delete, cancel and void) your ticket. For international, there is no functional online change flights search, it always gives some sort of error or other (such as "We are unable to complete your request Your request to reissue this ticket cannot be completed at this time. Please try again later." or "Let´s Try That Again We´re having some trouble completing your request right now. Give it another chance and start over. If that doesn´t work, contact us for help. Message # 7000").