You have to do several things:
1. To change the name, set the name in the project-properties about, in Constrcut 2. That should change the name in the Task-Manger or in the window if you use the windows-mode.
2. The Taskbar icon.
That is not so easy. I can only say how to do it in Windows 7.
Make a png of your icon you want in 128x128 pixel. Put it in Program Files\Construct 2\exporters\html5\icons and rename the the old icon_128.png in something like icon_128.old. Rename your icon png to icon_128.png.
Now you have to restart Construct 2. After exporting your game, you should now have the new icon. You have to change it back to the old icon or every game you export with NWjs has this icon.
You can also change in the package-win.json or package.json in Program Files\Construct 2\exporters\html5\nwjs (don't know exactly which one) the logo name with your icon png and put your png in the directory with the icon pngs.
3. use resource hacker to change the icon of the game self.
You do all of this at your own risk. Please don't blame me if Construct 2 doesn't work correctly anymore.