install new mainboard and let windows 10 have a fun booting, chances are high that it will just boot
later you can uninstall old drivers and then add new ones
i did that wiht my last mainboard update, that also came with new cpu, it worked
if it doesn't work, you can reinstall, leaving all the files in there, that way you don't loose the documents and settings and stuff like that
about the windows 10 license, it will ask you to activate because the activation process depends on the mainboard, and you change it so it gets deactivated so you might need to enter the serial key again but if it is a digital rights license you might need to link that license to your hotmail, live or outlook mail account and log in to windows 10 with that, should also end activated again
it depends on what windows license you have