Thanks for posting here, Heather. Let me be the first to welcome you here in the Community.
Before anything else, are you trying to update the sign-in information on the Banking page or App Transaction section?
If you're referring to the account information connected to QuickBooks on the Banking page, you can follow these steps:
Click Banking from the left menu.
Select the Edit ✎ icon for the bank account you want to update.
Choose Edit account info.
Enter your updated bank info and click Save and connect.
After that, the system will attempt to connect with your bank to verify your information. Select I'm done, Let's go! once you see a confirmation message. You may utilize this article for detailed steps: Update your bank account sign-in information.