clicking on buttom using httprequest in vbs : I WANT TO SIMULATE 'ie.document.getElementbyId("buttom_id").(0).click' IN XMLHTTPREQUEST, PLEASE HELP :(

THEREFORE IN CLICKING THE BUTTOM :
1) RIGHT CLICK ON THE WEBPAGE AND SELECT 'INSPECT'
2) SELECT NETWORK TAB
3) COPY ALL AS HAR

THIS INTERACT IS IN below:
[HAR FILE][1]


  [1]: http://textuploader.com/dr1bt

MY CODE IS BELOW:

    Function SaveGraphImageFromURLs( fileUrl, filePath)

    Dim FileNum As Long
    Dim FileData() As Byte
    Dim WHTTP As Object

    fileUrl = "http://80.191.214.122/Orion/Charts/CustomChartData.ashx?Calculate95thPercentile=True&CalculateTrendLine=True&ChartDateSpan=1&ChartInitialZoom=yesterday&ChartName=MMAvgBps&ChartSubTitle=%24%7bZoomRange%7d&ChartTitle=%24%7bCaption%7d&Height=0&NetObject=I%3a21067&ResourceID=69&SampleSize=30&Width=640&DataFormat=ChartData&NetObjectIds=21067"

    WHTTP.Open "post", fileUrl, False
    WHTTP.setRequestHeader "Content-Type", "application/x-www-form-urlencoded"
    WHTTP.send

    FileData = WHTTP.responseBody
    Set WHTTP = Nothing

    'Save the file
    FileNum = FreeFile

    Open filePath For Binary Access Write As #FileNum
    Put #FileNum, 1, FileData
    Close #FileNum
    Debug.Print "File has been saved!", vbInformation, "Success"
    End Function