Suppose an excel file is created by my shopping cart every day,the file contains order details on that day

The excel file contain 3 field, namely:

1: order number

2: first name

3: last name

when the file is imported to filemaker:

1: if the order number in the excel files exists in one of the filemaker record, filemaker will UPDATE that record

2: if the order number in the excel files dont exist in any filemaker record , a new record is CREATED

May I know how I can do this?

Thank you

Right now, when I import the excel file by:

File---Imports Records----File

The records in that excel file are imported into filemaker while the existing records in the filemaker are all deleted......

This is not what I want....