Import and update data simultaneously

I have a custom table with AN8 as the primary key. I use this table as a temporary table for importing large amount of data like bank account no, address etc. Now, while importing data from excel, I want to highlight the duplicate records. For example, importing record with AN8=2563 which is already exist in the table. As AN8 is the primary key, it will tell about the duplicate while clicking OK.I want a different functionality. If the record to be exported is already exist in the table, I want to update with the new values. How can I accomplish