If it's JUST stiff, you might get by with cleaning/greasing.
If it 'snicks' or has a detent with front end pointing straight ahead, the bottom one likely requires replacement.
Top one falls out..bottom one is pressed onto the stem. You'll have to take it to a shop to have it pressed off (if pressing is the choice and you don't have one). One poster got his off with a big hammer and screwdriver..but he was a bearing person by trade. Probably knew some tricks.
I cut mine off with an air tool. Put a new one back one with a piece of pipe (1 1/4) and a sledge (2 1/2#). Seems bearing was around $30 or so from a kawi dealer.
If you have a bad one, you'll be happy with the handling once you get the new one on.