Type 'vv' or 'vg' for visibility graphics dialogue box. Once open, click 'Object Styles' button. The difference between Object Styles and Visibility Graphics is that visibility graphics applies only to the view you are in, Object Styles applies to the whole project. Make a change and click apply to preview what line weights you are changing, if you don't see any lineweights changing, make sure 'Thin Lines' is not toggled on 'tl'. Thin lines will toggle off lineweights and show all lines as thin lines for practical purposes of designing with Revit. The Thin Lines feature does not change lineweights of print views.