Just wind it up as high as it'll go and then wind it up a little more.
You didn't mention any specifics like mother board etc. so no one will be
able to say without that. TO go from 1667 to 2000 you'll need a very stable
board, proper power supply and really great cooling. You'd need to advance
the multiplier from 12.5x133 to 15x133. Good luck with that.