This function gets the series names, puts them into an array, sorts the array and based on that defines the plotting order which will give the desired output.
Function Increasing_Legend_Sort(mychart As Chart)
Dim Arr()
ReDim Arr(1 To mychart.FullSeriesCollection.Count)
'Assigning Series names to an array
For i = LBound(Arr) To UBound(Arr)
Arr(i) = mychart.FullSeriesCollection(i).Name
Next i
'Bubble-Sort (Sort the array in increasing order)
For r1 = LBound(Arr) To UBound(Arr)
rval = Arr(r1)
For r2 = LBound(Arr) To UBound(Arr)
If Arr(r2) > rval Then 'Change ">" to "<" to make it decreasing
Arr(r1) = Arr(r2)
Arr(r2) = rval
rval = Arr(r1)
End If
Next r2
Next r1
'Defining the PlotOrder
For i = LBound(Arr) To UBound(Arr)
mychart.FullSeriesCollection(Arr(i)).PlotOrder = i
Next i
End Function