How to replace currently running EXE with EXE from web site?

The following code downloads the latest program release from our web site.  The problem is, I need to download the currently running EXE file...therefore it needs to download and replace itself.  

I've renamed the file at the web site to program.ex_ and downloading that file to the current folder works OK.

QUESTION...
How do I replace the running EXE with the revised EX_ once the download is complete and the program is still running.

CODE...
Private Declare Function URLDownloadToFile Lib "urlmon"_ Alias "URLDownloadToFileA" (ByVal pCaller As Long, ByVal_ szURL As String, ByVal szFileName As String, ByVal_ dwReserved As Long, ByVal lpfnCB As Long) As Long


If getUpdate = 1 Then
    OKToDownload = MsgBox("Download latest program_ update ?", vbOKCancel)
    If vbOK Then
       If SaveURL_("http://www.somewhere.com/downloads/program.ex_", "c:\programDir\program.ex_) Then MsgBox "Download complete!"
    Else
       MsgBox "Download cancelled"
    End If
 End If
End Sub

Public Function SaveURL(ByVal sURL As String, ByVal_ sFileName As String) As Boolean
   sfile = App.Path & "\program.ex_"
   SaveURL = URLDownloadToFile(0&, sURL, sfile, 0, 0)
End Function