To extend the range of the SUM formula:
1. In cell C7 insert the SUM formula with the total for range A1:A5.
2. Select cell C7.
3. Press F2 to enter edit mode.
Click any place within the formula in the Formula Bar.
4. Drag the handle of the range to extend the range (the handle is located in the bottom-right corner of the range).
5. Press Enter.
Screenshot // Extending the Range of the SUM Formula