Normally the Excel column formulas get updated or refreshed automatically. There is one option in Excel to update the columns automatically.
In Excel 2003: Tools -> Options -> Calculation. Make it Automatic for automatic refresh functionality.
In Excel 2007: Formulas -> Calculation Options -> Automatic/Manual. Make it Automatic to refresh the columns automatically.
Suppose if your calculation options set as manual and after making the calculation options to automatic, still your columns are not getting updated automatically. In this scenario you can use below mentioned key combinations to do the column refresh.
F9 : Refresh the columns and depended columns in workbooks.
SHIFT + F9 : Refresh the columns and depended columns in Active worksheet.
CTRL + ALT + F9 : Recalculate all the formulas in all open workbooks
CTRL + ALT + SHIFT + F9 : Recalculate all depended formulas, formulas in all open workbooks.