When I upgrade a preinstalled (OEM) or retail version of Windows 7 or Windows 8/8.1 license to Windows 10, does that license remain OEM or become a retail license?
If you upgrade from a OEM or retail version of Windows 7 or Windows 8/8.1 to the free Windows 10 upgrade this summer, the license is consumed into it. Because the free upgrade is derived from the base qualifying license, Windows 10 will carry that licensing too.
If you upgrade from a retail version, it carries the rights of a retail version.
If you upgrade from a OEM version, it carries the rights of a OEM version.
What happens if I change my motherboard?
As it pertains the OEM licenses this will invalidate the Windows 10 upgrade license because it will no longer have a previous based qualifying license which is required for the free upgrade. You will then have to purchase a full retail Windows 10 license. If the base qualifying license (Windows 7 or Windows 8.1) was a full retail version, then yes, you can transfer it.