Model: Zenith Notebook 433Lnp+
Operating System: All Windows Versions (Note: might work with other versions of this os.)
Press enter at "Advanced configuration" and choose Boot Option "Enter Monitor MFM300", exit BIOS setup and boot.
In monitor mode, choose option 5, "BIOS update". Your version number is stated here. Probably you can update your bios from here, after having unzipped the zip-file, and also autoextracted the resulting *.EXE file on a disk first.
You may also run the BIOS update from the disk. (Probably fupdate.exe with parameters, long ago since I updated my computer, don't remember the details... -) ) To get out of the monitor mode, choose the option "boot command" and choose your harddrive or floppy. Boot. Get back to your BIOS setup and choose to boot normally via the menus that I described first.