If it's a BIOS update and if you interrupt it chances are it may cause a damage or may brick the laptop causing it not to boot up but in times like that the laptop being frozen your last option would be to do a hard reboot. Do try opening Task Manager first and see if you can cancel the update. Press CTRL+ATL+DEL and it should open Task Manager, close the update that is running. If it will still not work your last option would be to do the hard reboot, press and hold the power button until it completely shut down. Power it back on and once it boots up do try reinstalling BIOS update again.