ho scritto una pagina che mi realizza l'upload di file img sul server

sembra tutto funzionare ok ma se sul server è presente un file con lo stesso nome del file appena inviato al server

il file originario non viene sostituito come posso ovviare?
il mio codice è questo:
codice:
Sub BuildUploadRequest(RequestBin)
	PosBeg = 1
	PosEnd = InstrB(PosBeg,RequestBin,getByteString(chr(13)))
	boundary = MidB(RequestBin,PosBeg,PosEnd-PosBeg)
	boundaryPos = InstrB(1,RequestBin,boundary)
		Do until (boundaryPos=InstrB(RequestBin,boundary & getByteString("--")))
		Dim UploadControl
		Set UploadControl = CreateObject("Scripting.Dictionary")
		'Get an object name
		Pos = InstrB(BoundaryPos,RequestBin,getByteString("Content-Disposition"))
		Pos = InstrB(Pos,RequestBin,getByteString("name="))
		PosBeg = Pos+6
		PosEnd = InstrB(PosBeg,RequestBin,getByteString(chr(34)))
		Name = getString(MidB(RequestBin,PosBeg,PosEnd-PosBeg))
		PosFile = InstrB(BoundaryPos,RequestBin,getByteString("filename="))
		PosBound = InstrB(PosEnd,RequestBin,boundary)
			If  PosFile<>0 AND (PosFile<PosBound) Then
			PosBeg = PosFile + 10
			PosEnd =  InstrB(PosBeg,RequestBin,getByteString(chr(34)))
			FileName = getString(MidB(RequestBin,PosBeg,PosEnd-PosBeg))
			UploadControl.Add "FileName", FileName
			Pos = InstrB(PosEnd,RequestBin,getByteString("Content-Type:"))
			PosBeg = Pos+14
			PosEnd = InstrB(PosBeg,RequestBin,getByteString(chr(13)))
			ContentType = getString(MidB(RequestBin,PosBeg,PosEnd-PosBeg))
			UploadControl.Add "ContentType",ContentType
			PosBeg = PosEnd+4
			PosEnd = InstrB(PosBeg,RequestBin,boundary)-2
			Value = MidB(RequestBin,PosBeg,PosEnd-PosBeg)
			Else
			Pos = InstrB(Pos,RequestBin,getByteString(chr(13)))
			PosBeg = Pos+4
			PosEnd = InstrB(PosBeg,RequestBin,boundary)-2
			Value = getString(MidB(RequestBin,PosBeg,PosEnd-PosBeg))
		End If
		UploadControl.Add "Value" , Value	
		UploadRequest.Add name, UploadControl	
		BoundaryPos=InstrB(BoundaryPos+LenB(boundary),RequestBin,boundary)
	Loop
End Sub
Function getByteString(StringStr)
 For i = 1 to Len(StringStr)
 	char = Mid(StringStr,i,1)
	getByteString = getByteString & chrB(AscB(char))
 Next
End Function
Function getString(StringBin)
 getString =""
 For intCount = 1 to LenB(StringBin)
	getString = getString & chr(AscB(MidB(StringBin,intCount,1))) 
 Next
End Function

byteCount = Request.TotalBytes

RequestBin = Request.BinaryRead(byteCount)
Dim UploadRequest
Set UploadRequest = CreateObject("Scripting.Dictionary")

BuildUploadRequest  RequestBin

contentType = UploadRequest.Item("blob").Item("ContentType")
filepathname = UploadRequest.Item("blob").Item("FileName")
filename = Right(filepathname,Len(filepathname)-InstrRev(filepathname,"\"))
value = UploadRequest.Item("blob").Item("Value")

'Create FileSytemObject Component
Set ScriptObject = Server.CreateObject("Scripting.FileSystemObject")

'Create and Write to a File
Set MyFile = ScriptObject.CreateTextFile(Server.mappath(folder)&"\"&filename)
 
For i = 1 to LenB(value)
	MyFile.Write chr(AscB(MidB(value,i,1)))
Next
 
MyFile.Close

%>

<html>
<head>
	<title>UPLOAD FILE</title>

</head>
<body>







<table border=0 width=360 bgcolor=#999999 cellspacing=1 align=center>
	<tr>
		
    <td width=400 align=center bgcolor=#669933><FONT FACE="tahoma" color=#ffffff size=2>Il 
      file <%=filename%> è stato uploadato con successo.</FONT></td>
	</tr>