But a more conventional way of doing what you say is to select the
"edit properties" tool, and when the properties window comes up,
specify "change width to 40 mils" and just click on all the traces you
want changed. Click, click, click, click, four traces done.
This is a conventional, pre-GUI-aproach. With modern GUIs, you first
select the objects to modify and then perform operations on your
selection. So you would first select one or more traces (Click,
Ctrl-click, Ctrl-click, Ctrl-click) and then select change width->40.