update records on importing file

Hi!
I can import a csv file into a table with success.
But if I try to import again the same csv file (edited a bit) I get an error because the primary key of the rows are already into the table of the db.

For ex. this is the content of the csv file I can import with success (the first value is the primary key):
"1","Jack","Cat"
"2","Goofy","Dog"

Then I edit that csv file:
"1","Tom","Cat"
"3","Jerry","Mouse"

I would like to reimport this file with the following behavior:
row 1 is updated and row 3 is added.

How can I do?
I'm using pgAdmin3.

Thank you in advance for any answer.