In the Home window,
on the Setup menu, select Settings. Click
Company, Sales Taxes,
and then Tax Codes.
Click Assign Tax Codes.
In the Show section, select either Customers or Vendors to display the type of records you want to update. From the With This Default Tax Code list, select the old default tax code that you want to update.
From the New Default Tax Code list, select the new tax code.
In the Name column, select the records that you want to update. You can hold down the CTRL key and use the left mouse button to select multiple records, or click Select All if you want to update all the records in the list.