Diagnosis
These routers do run warm—it's a compact box with a processor and radios working hard. Warm is normal, but 'really hot' (uncomfortable to hold) can indicate a ventilation problem.
How to Fix It
Improve airflow. Make sure it's sitting right-side-up (logo facing up) on a hard, flat surface. Get it off carpet, out of any cabinet, and away from other heat sources like a modem, game console, or direct sunlight. A few inches of clear space on all sides makes a big difference.
If That Didn't Work
Check what's running. Heavy features like continuous VPN (VPN Fusion), persistent torrenting with high connections, or a constantly busy NAS can push the CPU harder. Consider disabling features you aren't using, like the media server or Traffic Analyzer history.
Heads Up
While the router is designed to throttle performance if it overheats, consistent high heat will shorten its overall lifespan. If it's still scorching hot with good ventilation and normal use, and especially if it's rebooting itself, it might have a faulty thermal pad or fanless design flaw, and you should look into an RMA.