A two-story home in Arizona with an open gallery is the worst possible situation. If the walls are poorly insulated and there are cheap windows (which is normal in the southwest), it can be difficult to manage temperature.
I would recommend the following:
First, set the temperature on the second floor 7-8 degrees lower than the first floor at night. The idea is that the second-floor unit will run double time and the cool air will "fall." The lower-level unit will not run.
Second, verify each bedroom has return air vents and keep the bedroom doors closed at all times. If there are no return air vents, make sure there is a 1 to 2-inch gap under the bedroom doors. You need the same amount of return vents or gap under the doors as the supply vents (in square inches); otherwise the rooms will pressurize and will stop cooling. When the doors are closed, see which rooms get hotter and try to adjust the supply vents to even out the upstairs temperature.
Third, have the A/C units checked for refrigeration levels. I have seen systems get low even though they are not leaking. If the systems are not charged, you will never cool the house, but you'll spend tons of money.
Fourth, if all else fails, consider purchasing a portable room A/C for the bedroom you sleep in. The idea here is just cool the space you need to.