Pretty common issue with one system, two story home. The dampers can be messed with, you can check for crushed/detached duct, but most likely it's just bad airflow that happens almost all homes with your set up. You can zone it, it's not cheap once the boards and dampers and installation all gets added up. Another option would be a mini split system, research them a little, they're gaining popularity. Or you can go more expensive and put an air handler in the attic with duct work and make your upstairs plenty cool