Steps to upgrade through ESXDOS (use attached files):
- Use a SD with working ESX-DOS 0.8.6 beta4 installed
- Copy FLASH.ZX1 on the root dir, UPGRADE on the BIN dir into the SD
- Boot with "Rooted 48K"
- Write .UPGRADE in the command line (remember initial dot)
- Wait the progress. After finish reboot your ZX-Uno
If all is ok you'll have v0.50 BIOS. Next upgrades can be done using BIOS because they are safe.