SQL column goes from first to last position in output
In the Columns page on the OLE DB Source, you can use the check boxes beside the columns to change the order.

The columns are added to the output in the order in which they get checked, so what you need to do is uncheck all the columns, and then check them again in the correct order.

Downstream data flow tasks will want to update themselves because the column mappings "broke", but this shouldn't be a big issue to fix.