This is an unpleasant task you should never have to do, unless we get a new plotter. You don't even have to do it then.
On the Options menu, All Pens And Colors. You get this:
A pen has two attributes, color and width.
Set the width using the field marked "Pen". Make sure the units are mm, not Pt (points).
To change the color, double-click the pen's square in the grid, or select it and click "Edit Color". I recommend using the HSB sliders to edit color.
You can select multiple pens at once and edit their color or width together. Cmd+click on pens to accumulate them, or Shift+click to select a range. Like a lot of things.
Selecting all the pens between 21 and 141.
Editing pens in ArchiCAD is similar, but we can use Attribute Manager instead.