I have the following question

When i have a sheet with the following data:

cell A1 1
cell A2 2
cell A3 3
cell A4 =sum(A1:A3) == 6


When i want to insert in row 4 another value (let's say):
cell A4 4

Then in cel A5 is still the formula =sum(A1:A3).

Is there a trick to let the formula change (automattically, e.g. with a key
combination) when inserting a row into == =sum(A1:A4)

I am using Office Excel 2003