system installation - Dual boot with windows 10 (upgrade from Win 8.1 OEM)

I have dual booted my laptop with windows 8.1 and Ubuntu 15.04. Windows came as a OEM with the laptop so I didn't delete it as I paid for it and I am not using it though. I want to know if I do the free upgrade to Windows 10 will it destroy my Ubuntu partitions? or will it mess up anything in the boot files or grub?