Upstairs Is Always Hotter Than Downstairs

Has anyone else had this problem? My downstairs feels comfortable, but the upstairs is always noticeably warmer, especially when it’s hot outside. Even when I lower the thermostat, the temperature upstairs doesn’t seem to improve much. I’m wondering if it could be an airflow issue, blocked vents, or something wrong with the ductwork. Has anyone found a solution that actually worked?