Squirt some penetrant at the retaining nut. Then loosen the bolt at the top center of the stem a couple of turns, tap it down and the stem should rotate. If so, pull it out.
Use a small punch or flat bladed screw driver to tap the retaining nut free. The spacer washer should lift out and you should be able to hand unscrew the large flat bearing retainer. Have a pan there to catch the ball bearings as they may not be caged. They will come pouring out the top and the bottom.