HELP: Cannot Change UEFI to Legacy Option in BIOS

I am trying to update my X51 BIOS vA01 to the latest A14.

I have to boot with an USB flash drive with DOS.

When I try now, it just boots into windows and ignores the drive.

I read that this is because of the UEFI and I need to disable (change to legacy) in BIOS.

The option in BIOS is greyed out. I see it, but it is permanently selected as UEFI.

Is there some other way to upgrade the BIOS (in windows not doc perhaps)? Is there some way to boot to DOS USB with UEFI (I am reading no online)?

Help!