Large Scale De-duplication

Large Scale De-duplication

We have 25K records in our lead file and 5K are duplicates.  I have downloaded the complete database and all the files.  I then opened the lead file and removed the duplicates.  I now have a clean file.

I want to remove the old lead file from CRM and replace it with this new clean one.  How do I do that?

I'm open to another way...  Just don't know how to be effective on this larger scale problem.

By the way...  The De-duplication tool was good only to a degree.  Once the absolute matches were resolved automatically, each of the rest of the files required an individual arbitration of which lead record was to remain.

I have too many duplicates to manage them individually.