First, unplug the monitor power cable from the electrical outlet. This is a critical safety step.
Next, use a clean, soft cloth that is only slightly dampened with water. Gently wipe the screen and chassis. If you have it, a screen-cleaning tissue or solution made for Dell monitors is ideal.
Do not spray any liquid directly on the monitor. Apply it to the cloth first. Never use detergents, ammonia, alcohol, abrasive cleaners, or compressed air, as this can cause permanent damage like color fading or peeling and voids the warranty.