You can change the bank details in the app or online under Balance and Payments tab, direct debit details, and you can certainly add son's name as described below but I'm unsure if it's possible to change the account holder only to another name. That may require setting up a new account, and is the email address for the account yours or your son's (just reminding you in case that needs to be changed too)
You will need to go to help, ask wattbot, type message the team, and ask there.
Replies not instant, circa 24 hrs (not weekends).
(By the way as this is a public community I've flagged your post as it has personal info in it )