Here is some illustrative code of how you might change the shape heights.
It assumes that the new values are in sheet 'New' (**Edit to suit actual**) and cells A2, A3,...... A16 and that the relationship between rectangle height (Points) and cell value (Gallons ??) is 1:10
If you put e.g. a value of 300 in cell A2, 600 in A3, 900 in A4 then it will set the first three rectangles with heights of 30 points 60 points etc.
Maybe try it out but ultimately you will need to code for both the correct source of tank values and determine the correct relationship of rectangle height to tank value.
Application.ScreenUpdating = False
Set ws = ActiveSheet
For Each shp In ws.Shapes
bot = shp.Top + shp.Height
shp.Height = Sheets("New").Range("A2").Offset(ros, 0) / 10 '10 cell value units per shape height point
shp.Top = bot - shp.Height
ros = ros + 1
Also you may need to check that the shapes in the for she loop do loop in the expected order as this can sometimes get out of sync depending upon how the shapes have been generated / edited.
Hope that helps.