After you file

If you no longer have the same phone number how do you even log-in to you're account to change it to the new phone number when everytime you try to sign into you're account it wants to send a confirmation text message to even log-in to the old phone number I'm trying to change....which again I don't have anymore so I can't recieve the text confirmation to even log-in.....so how do I change my phone number then?