That plant is either suffering from dry soil conditions or soggy wet soil conditions for an extended period of time. It may need now to be moved to the next larger size pot. This would make watering easier and give the roots room and soil to grow in. After repotting begin to feed the plant with a soluble plant food such as Miracle Gro at the label rate. This should result in new healthy growth although the old yellow leaves may not improve but could be removed in time.
Q&A Library Searching Tips