provided you only have all "copy of" files and not their originals, here's a vbscript
Set objFSO= CreateObject("Scripting.FileSystemObject")
Set colFolders = objFSO.GetFolder("C:\test")
For Each oFile In colFolders.Files
If InStr(1,oFile.Name,"Copy of",1) > 0 Then
newName = Replace(oFile.Name, "Copy of ","")
oFile.Name= newName
WScript.Echo oFile.Name
End If
Next