refund

You can only change your Bank Account Number if you had a refund failure i.e your IT Return is processed and a refund was generated for you but you did not receive it.
If you wish to change the Bank Account Number for Refund failure case, then login in the Income Tax e-Filing website and go to 'My Account' → 'Refund re-issue request'. Select the mode through which you wish to receive the refund- ECS or Cheque. Enter the new Bank Account Number and provide address details. Submit the request.

Once the request is submitted, your new Address is updated with the Income Tax Department.