Mike S. wrote:
I have central air in my house and the unit and everything is about 20
y/o. I realize it should be updated but I have no control over that.

The problem I have is that if I set the thermostat to to 70 degrees
fahrenheit, then the downstairs stays about 70. But the upstairs will
be anywhere from 76-80, depending on the room and how hot it is
outside. So the problem is that people complain that it's too cold
downstairs and too hot upstairs. Ideally, I would like it to be about
76-78 downstairs and about 74 upstairs.

Why does this happen and is it normal? I know that a lot of air blows
out in the vents downstairs and not a lot blows out upstairs. I shut
off all the vents that aren't needed and close the doors to rooms that
aren't used. I have the fan set to "auto". I don't know if leaving it
on auto is better than setting it to "on". I don't like to mess with
it because it seems to cause problems with it.

Any opinions or suggestions (other than buy a new unit)?

It sounds like the t'stat is doing exactly what you have asked it to do.
Problem is with moving hot air out of upstairs. Any way to set up a
small exhaust fan operating on a t'stat for the upstairs? 70 is darn
cold, IMO. Depending on how the house is arranged, and the room for
more air flow, perhaps a ceiling fan upstairs (in stairwell?) to move
air up or down as needed to get temp more balanced