If you current bios allows to create Ubuntu entry, then just set it first in boot sequence. If there is no Ubuntu entry in UEFI, then why are you afraid that it is removed?
If Bit Locker is not suspended, the next time you reboot the system it will not recognize the Bit Locker key.
This article will guide you through the steps of checking for updates, backing up your personal information and creating an all important system image. Windows 10 requires the same minimum hardware requirements as Windows 7.
Those requirements are: You can also check to see if your machine is capable of running Windows 10 right from your desktop.
I changed the Windows 8.1 product key to a Windows 8 Pro product key and did the upgrade.
I checked to make sure it was activated, and it did activate online.