Create Charts/Based On ListBox Value

i am having a problem of updating my graphs in the application i devloped, my application is like this, go to sheet 1 click showuserform button and suer form contains combo and list box select the sheetname in the combo and select two values in the list and click plot.it plots the graphs acording to the selected values but my problem is it makes a newchart every time when we select a new week range it is getting stacked...it is not getting updated with the most recently plotted graph ??? i am facing this problem when i am opening my application in other computer...u can see my problem when u open my application. i am attaching my workbook and this is the code i used for making the chart

Sub MakeChart()
Dim rng1 As Range, rng2 As Range
Dim gs As String
gs = ComboBox1.Value
Application. ScreenUpdating = True
'First selected
For i = 0 To ListBox1.ListCount - 1
If ListBox1.Selected(i) Then
Set rng1 = Columns(1). Find(ListBox1.List(i))
Exit For
End If
Next
'Last selected
For i = ListBox1.ListCount - 1 To 1 Step -1..............................