Right-click on the start menu icon and select Settings from the menu that opens up.
Xbox Live’s UI already does this and people pay $50/year for that. The problem is even though the taskbar background can be skinned, the window buttons can't be made to look like Windows 7/8.1. Here is why! To do the most with this, Windows 10 we can make changes to the taskbar for ease. I assume you are asking this for Windows 10? This opens the Classic Shell Menu settings.
