Test Cases are being replaced when imported to RQM frm Excel

Hi,

I have exported a few Test Cases from Excel to RQM using the RQMExcelImportUtility Tool.
After that I have made a few changes in the description steps and changed the Test Case Name and exported the new set from the excel sheet.

This time the old Test Cases imported previously were overwritten by the new set though the Test Case Name is different.

Is there something process to be followed while exporting from the excel sheet.
Can we edit the Same Excel sheet and export the Test Cases.

Can you please provide more details on exporting testcases from Excel to RQM.

Thanks
Teja