Changing the column order on this page only influences how the columns are ordered internally in the code. It does not influence how the columns are ordered on the Reporter Settings page, Report Editor or in the report.
It is generally only necessary to change the column order here if you have referenced a column in an expression, as any column referenced in an expression column must come before the expression column.
Expression columns that reference another column must have a higher number than the referenced column.
To change the column order: