how do you manually open and close the headlights on a 2000 firebird

There is a knob you can adjust them up, but once you start the car & shut it off they will try and close. So they are 2 fuse you can pull out and that will leave them up or where you adjust them too. I adjusted mine up so they wouldnt freeze down.

can you adjust them down to or just up

Either way, but if you don't pull the fuses it won't stay where you adjust them. There is a screw for adjusting the headlights up & down and one left & right when they are flipped up too.