Roller adjustment just seems to move roller laterally - not up or down

A quick learner from Florida says:
I was attempting to replace my aluminum glass sliding door's rollers, but could not figure out how the mechanism worked. The roller appeared to be simply held in place by the friction of the two contacts on the assembly and when "seated", was recessed too far in the assembly to be useful. The adjustment screw simply slide the roller back and forth and not up or down. Any suggestions on what I should be doing here? I had to button everything back up, so no pics are available.

The door appears to be original to the house, so it's about 20 years old.

It was a bear to remove, BTW.
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Tom from SWISCO responded:

Thanks for contacting us. Most patio glass door rollers are screwed on, but some others are further held in by the bottom door rail. You'll need to remove the door, place it on a flat stable surface, and remove the screws holding the door rail to the bottom. You then use a mallet and block of wood to gently tap it off. 

This is just an educated guess; there's a possibility you have some other design feature of your door holding your roller in that I can't predict. However the bottom door rail is the most common culprit when I run into this issue.

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