Updating Access from Excel

I have no problem adding new records to a customer database from an Excel spreadsheet using the import function. However, what I would like to do is to add data to an existing record in a table. My Excel spreadsheet column headings reflect the table field names, and I have tried entering the primary key of an existing record together with data in the field I want to update (such as a sales figure). Import doesn’t like it as it tries to add as a new record and obviously finds a duplicate key. Is there a way to handle these sorts of batch updates?