We only use the top floor for guests but we noticed that this week when we had guest over the downstairs stayed cooler (the rooms that get air last were much cooler) because we were cooling the upstairs what is the appropriate way to efficiently cool upstairs and down what temp should we set upstairs to if downstairs is 76?

It is obvious to me, because I know nothing about this, that cooling the upstairs would require more vents. Or your AC is not big enough to do the job for your house. What is your square footage ? And, by upstairs do you mean a second floor, or a third ?

Do you have 2 units and 2 thermostats?

Because cold air is denser and falls, you can typically set the upstairs at temp you want and lower floors a couple of degrees higher-assuming you have 2 units or at least zone controlled.

There are two units ant two thermostats main floor ( downstair) is 2000 sq ft upstairs 2nd level is 1500 sq ft upstairs unit is smaller than main floor

Was the temperature down stairs cooler than the set point on the thermostat?

No but the rooms that are usually hot were at the set point temp

Do you shut off upstairs unit when it is unoccupied? If so, I would leave it on all the time and set it to 82*.