How can the following code be modified to restrict the upload file type?

<%
Dim FormData, Formsize, divider, BCRLF
Formsize = Request.TotalBytes
FormData = Request.BinaryRead (formsize)
Bcrlf = ChrB (+) & ChrB (10)
Divider = LeftB (FormData, InStrB (FormData, Bcrlf)-1)
Function SaveFile (Formfilefield, Path, MaxSize, Savtype)
Dim streamobj,streamobj1
Set streamobj = Server.CreateObject ("ADODB. Stream ")
Set StreamObj1 = Server.CreateObject ("ADODB. Stream ")
Streamobj.mode = 3
Streamobj1.mode = 3
Streamobj.type = 1
Streamobj1.type = 1
SaveFile = ""
startpos = LenB (divider) + 2
Formfilefield = Chr (a) & Formfilefield & Chr (34)
If Right (path,1) <> "" Then
Path = path & ""
End If
Do While startpos > 0
strlen = InStrB (Startpos, FormData, Bcrlf)-startpos
Searchstr = MidB (FormData, startpos, strlen)
If InStr (Bin2str (SEARCHSTR), Formfilefield) > 0 Then
FileName = Bin2str (GetFileName (Searchstr,path,savtype))
If FileName <> "" Then
Filestart = InStrB (Startpos, FormData, Bcrlf & Bcrlf) + 4
FileLen = InStrB (startpos, FormData, divider)-2-filestart
If FileLen <= maxsize*1024 Then
Filecontent = MidB (FormData, Filestart, FileLen)
Streamobj.open
Streamobj1.open
Streamobj.write FormData
Streamobj.position=filestart-1
Streamobj.copyto Streamobj1,filelen
If Savtype =0 Then
Savtype = 1
End If
Streamobj1.savetofile Path & FileName, Savtype
Streamobj.close
Streamobj1.close
If savefile <> "" Then
SaveFile = SaveFile & "," & FileName
Else
SaveFile = filename ' shows the filename
End If
Else
If savefile <> "" Then
SaveFile = SaveFile & ", *toobig*"
Else
SaveFile = "*toobig*"
End If
End If
End If
End If
If InStrB (startpos, FormData, divider) < 1 Then