Edit Module Width

I would like to edit the left module position width to be smaller.. where do I change this?

In layout editor you can increase/decrease width by 1/12 of total content width.

Other solution is to use style (you could place it at bottom of template_css.css):

.mp_left{
width:XXXpx!important;
}

but we really don't recommend playing with layout in such way because everything is connected and maybe it will open Pandora box of needed changes after.