DIAGNOSIS Some warmth is normal due to the internal power circuitry and the LED backlight, but it shouldn't be uncomfortably hot to the touch. Excessive heat often points to it being driven at full brightness for an extended period or a poor ventilation setup.
FIX First, lower the monitor's brightness from the OSD (On-Screen Display) menu using the buttons on the side. This is the biggest factor in heat generation. Also, make sure the back isn't pressed flat against a soft surface like a bed or pillow, which traps heat.
IF THAT DIDN'T WORK Check what you're displaying. A static, all-white screen at full brightness will generate more heat than varied content. If it's hot even at low brightness with normal use, there may be a fault in the power regulation.
HEADS UP Continuous excessive heat can shorten the lifespan of the panel. If it's too hot to hold your hand on comfortably, turn it off and let it cool down, and consider running it at a lower brightness setting permanently.