Editing the North angle can only be done with the Pro version of SketchUp 8 or with a previous version of SketchUp. To enable the North angle, click View > Toolbars > Solar North
Likewise, there can only be one North angle used in a SketchUp file. If you need to display varying North angles, you can create separate files or use an older version of SketchUp.
This plugin isn't installed by default in SketchUp Pro 2013. You'll need to open the Extension Warehouse from within SketchUp, locate the "Solar North" plugin and choose "Install" to add this plugin.