Simply put, block the machine so the wheels can turn freely and lift the cab
Remove the steering linkages at the levers and the pintle arms on the hydrostatic pump. Remove the 4 bolts holding the stops to the big plate on the side of the pump, you will see a spring that puts pressure on this. Rotate the stops 180 degrees and put them back on, don't tighten them up. Start the machine and working from the back hold the stop against the pintle arm when the wheels do not move tighten the bolts up. Move it back and forth a few times and let it return to centre. If the wheels don't move its correct, if they move re-do the setup. With the back done, do the same to the front.
Its easy to explain, but it does take a bit of time to do.
To do the job rite, you should replace the pucks on the pintle arm, but the bolts are a pain to get to.
Make sure the back of the stops are not worn, they may hev been flipped already. You don't REALLY have to turn them over to get centre, you can still do it with worn bits, just do the steps i mentioned earlier. Make sure you start at the back! it will not work if you start at the front.
If anything isn't clear just let me know and i'll try to explain it better.