The Windows 10 Anniversary Update added a cool feature for DIY types: The ability to tie your Windows 10 license to your Microsoft Account, rather than to your PC's hardware. No more calling Microsoft support to activate your OS simply because you swapped out your motherboard.
If Windows 10 freaks out after you upgrade your PC, go to 'Settings->Update & Security', add your Microsoft account (if it isn't linked already), and then click 'Troubleshoot' at the bottom of the screen. Hit Microsoft's Account Troubleshooter FAQ for more info.
