I was given an older Precision M4600 (BIOS version A10) with a bad SSD and one bad SIMM.  I've replaced the bad parts, and want to install Windows 10 from a USB stick.  The USB image was built from a Windows .ISO with Rufus, which means it's unsigned and won't work with Secure Boot enabled.  I've been through the BIOS config at least a dozen times and can't find an option to disable Secure Boot - I can select Legacy/UEFI, set boot order in Legacy, but I can't find what I need.  I'll note that in UEFI mode, I cannot add, delete or view "Boot Options", so if it's somewhere under that, I need help with turning it off there.

Thanks!

Steve