Validate data from Excel before uploading it in SQL using C#

suppose i have above excel sheet which has only new data, then ok it will be uploaded easily

 

now I have this above excel which has new as well as old data(which is uploaded already)now how i can use validate it to import in SQL via C# file upload control.

 

 

now again suppose i have an excel which has records new data + old data(which is uploaded already) and + some modified data means suppose I have a invoice number of 1 july 2016 which was amount 10000, but it should be 100000.now today it is updated and now should be updated in sql..

please help me.thanks in advance