Without knowing if this is a general question or if you are experiencing an issue when you try to generate file, I'll run through a few setup items that come to mind.
Payroll Checkbook defaults are set at Microsoft Dynamics GP > Tools > Setup > Payroll > Payroll
The bank information should come from the checkbook setup (Cards > Financial > Checkbook). You can compare your new checkbook with your previous checkbook to see if you there is something missing/different.
I assume by ACH you are referring to the Direct Deposit file. This is configured at Microsoft Dynamics GP > Tools > Setup > Payroll > Direct Deposit, but I don't think it should need to be changed for a new bank account unless someone has customized the file.
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