can't update Dell Optiplex 755 BIOS

I got a Dell Optiplex 755 from a local electronics recycler. It came without an OS. I have several of these from the same source but they are in varying states, at least in terms of the BIOS version. Unfortunately, some of them have a very early BIOS version that lacks the hardware virtualization option.

To attempt to solve this, I've grabbed O755-A22.exe, put it on a USB drive, booted into a FreeDOS 1.03 Live CD, and attempted to run it. It fails with a message that the utlity cannot be used in a "protected environment." What can I do to mitigate this?