Yellowing leaves is a common problem for Aglaonemas, and it is often caused by overwatering. To prevent this, it is important to only water your plant when the topsoil is dry to the touch. During the winter months, it's okay to let your plant dry out a little more between waterings. When you do water your aglaonema, make sure to provide enough water so that liquid flows out of the drainage hole at the bottom of the pot and into the saucer. Be sure to discard any excess water in the saucer to prevent the roots from rotting due to overwatering.