Rename file before upload

Hi,

I want rename file befor uploaded,

I use this code, 

how to change it? please help me,

Dim str As String = Request.PhysicalApplicationPath
        Dim savePath, picPath As String
        savePath = ""
        picPath = ""

If (FileUpload1.HasFile) Then
            savePath = str + "pic" + "\" + fileName
            picPath = "~\pic\" + fileName
            FileUpload1.SaveAs(savePath)
            piclb.Text = "saved " & fileName
        End If