Hi Ram,
Customer attribute data once uploaded cannot be deleted unless the data source is deleted otherwise.
You can modify the schema by uploading a new file with the changed schema but the profile/customer id's once uploaded cannot be deleted.
Looking at your questions:
Question 1 : How to delete a particular record from data source ?
-- This is not possible. Customer attribute file upload either merges or updates the given record. But delete is not possible.
Question 2 : How to flush/erase all records without affecting customer attribute ?
--You shall have to delete the entire data source to erase all the records.
Regards,
Rachit