I have two spreadsheets

They are in the same format, ie.

A:A contain serial number
B:B contain product names
C:C supplier
D:D address
....
....


The two spreadsheets are regularly update by me and my bussiness partner in
another country.

However, when I get the file from my partner, her spreadsheet may contain
some new entries.
If I just copy and paste her spread sheet into mine and there will be some
items being double entry.

How can I delete the double entries after copy and paste?

Thanks