it is easy, eyeglasses get foggy because of steam or water. Just use a soft cloth to wipe it out from the lenses. If you want to prevent your eyeglasses from foggy and cloudy, you'd better keep far away from high temperature places. Also, i heard that there is a type of coating for eyeglasses that can stop the lenses from foggy. You may consult an optician in glasses shop.
First, rinse both sides of your eyeglasses lenses under warm water. Second, make the a microfiber rag wet with warm water and drop a small amount of mild dish soap on the rag. Then, use the rag to wipe both sides of the lenses in a circular motion gently. Finally, dry the lenses with the another dry and clean rag. In this way, your eyeglasses are less likely to get foggy and cloudy.