How to fix one room being hotter than the other?

Correcting a situation where one specific room in your home is noticeably hotter than the rest of the house requires a systematic approach to airflow and thermal management. First, inspect the supply and return vents in that warm room to ensure they are fully open, unblocked by furniture, and clean. Second, adjust your HVAC system's duct balancing dampers in the basement or crawlspace to restrict excessive airflow to overly cool rooms while opening dampers wider for the warm, distant space. Third, combat solar heat gain by installing blackout curtains or reflective window films on west-facing windows that absorb intense afternoon sunlight. Fourth, check your attic insulation levels directly above that hot room. You can troubleshoot airflow velocity using an anemometer. You can verify that your corrective actions were successful when room-to-room temperature differences equalize within a comfortable range.