On Windows: right-click the desktop > Display settings > Advanced display > choose your monitor and see the current refresh rate. Use the dropdown to change it — if your monitor supports 144Hz but shows 60Hz, select the higher rate. Make sure you're using a cable that supports the rate (DisplayPort for high refresh, HDMI 2.0+ for 120Hz+). On Mac: System Settings > Displays > select your monitor > check the Refresh Rate dropdown. Some MacBooks only show higher rates (ProMotion 120Hz) when not in battery saver mode. To verify the actual refresh rate, use an online screen test with a motion test pattern — you'll see smoother motion at higher rates. After changing the rate, reboot and run the screen test again to confirm. Gaming monitors may require enabling the higher rate in the monitor's OSD (on-screen display) menu first.