Remove the steering box, there is 3 or 4 large bolts that hold it to the framerail and disconnect the input shaft. You will probably need a pitman arm puller to get it off the steering box splines. Mark where everything was aligned before you take anything apart.
Do what ohsofly said above. I did mine on my 84 and it was a little tricky. I used a 33mm socket and breaker bar to get the nut that holds the pitman arm to the steering box and then just put the pitman arm puller on there.