Easiest way to recenter the steering wheel is to adjust the drag link. You can do this with it still attached to the pitman arm. A more precise and less frustrating way is to pop the drag link off the pitman arm, recenter the wheel, adjust the drag link so it fits exactly up to the pitman arm and reattach it to the arm.
Like Redford said either take it to a shop to find out why it was upside down or do a bit of inspection of your own. It could be someone replaced the steering box or some other steering component and never adjust the steering wheel. Or maybe something more foul is afoot.