If you'd like to update the billing details of your Acrual Subscription, like which Direct Debit account your payments come out of, you can easily update this via the Acrual Account settings page.
Firstly you'll need to login under the account holder user account (the user details that your account first signed up with). The account holder is the only account who will have permissions to update the billing details.
Once logged in, you can navigate to the "Account Settings" page using the drop down menu in the top right corner.
On this page, go to the "Subscription / Upgrade" tab and you should see a button that says "Edit Card" next to the current card details. Click this button and fill out the form with the new Direct Debit card details you'd like to use going forwards.
The updated card details will be used going forwards, and will take effect on the next subscription payment.