On a desktop, navigate to the dashboard you wish to modify. You are then able to click the widget and drag them from column to column. You can also do this to re-order the widgets within a column. Once you are done with your re-ordering your changes are not saved until you click on Save Changes within the notice that appears when you change the order of your widgets.

Note that you cannot change the order of widgets on system dashboards. You are also unable to change the order of widgets using a mobile device as this is not a good user experience.