Import spredsheet data to existing list.

I have excel sheet and existing sharepoint list(Impor spredsheet app) on the sharepoint server. We need to append the data from the new excel sheets to the existing lists items of the sharepoint list. Can you please provide some ideas on how to provide a solution for this? Let say I have 100 records in one excel file. I have imported that file to spredsheet app. It works fine for first time. Now I have 100 records in that list. Now user has added 10 more records in that excel sheet. That 10 records I have to appends to the list which is created very first time.