I did this in 2016 - hope this helps. Details from 2016 - I have just been through the same process. Go into Account, Payout Preferences, Add Payment Method, put in your address, Next, click on Bank Tranfer, next - then click next again - this will direct you another web site to put in your new bank details. Your old bank details will remain as default but when you have your next guest & Airbnb try to put it into your old account - they will then send you another email later with a connection to change your new bank account to default. I was not able to change my new bank details to default by myself but this worked very easily - it just takes a few days after your next stay.