As you update the table it will automatically update the heading as well. In order to get the correct number format use the TEXT function and specify the number format that you want to display. In the Number format list box choose a format for the numbers.
Insert a formula in a table cell.
On the Table Tools Layout tab in the Data group click Formula. In the Formula dialog box enter the formula. Click the blank cell you want to show the calculated result then click layout Formula. Add to formula with Kutools for Excel.