The firm puts pollster and political adviser Mark Penn in charge of strategy but does not indicate what his new role will entail.
Tony Bates and Tami Reller prepare to exit the firm as Satya Nadella takes over as CEO.
The company aims to reach a wider audience for Windows Phone by turning to cheaper chipsets and easing restrictions on how phone makers use its software.
The relatively slow sales of Windows 8, and its latest incarnation Windows 8.1, reflect a steady two-year decline in PC sales.
Microsoft's upgraded version of Windows 8 could restore the OS to its former glory.
Although sales are keeping pace with those of Windows 7, Microsoft is looking to tweak the new system to boost usability.
With new touch-screen devices on the way, Microsoft expects a surge in sales of Windows 8 software.
Microsoft's new operating system has made a solid but unspectacular start since its launch 10 weeks ago.
The Windows 8 upgrade momentum is outpacing that of Windows 7, but there's still a long way to go, says Microsoft.
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