May I change my bank account number after filed my tax?

[Carl]

Nope.  If your return has already been transmitted to the IRS, and they've accepted it, you're done.

If the account you're having your refund go to does not exist, or is not "valid" (meaning that for a joint return, BOTH names must be on the account), then when it's rejected back to the IRS, they will cut a paper check and mail it to the address on your tax return. That can take 6-8 weeks or longer before you get the check, in this case.