Reprogramming of sensor networks is an important and challenging problem, as it is often necessary to reprogram the sensors in place. Recently, increasing research attention has been directed towards wireless sensor networks. Wireless sensor networks consist of collections of small, low-power nodes that interface or interact with the physical environment. Wireless sensor networks facilitate monitoring and controlling of physical environment from remote locations with better accuracy. They have applications in a variety of fields such as environmental monitoring, military purposes and gathering sensing information in inhospitable locations. Sensor nodes have various energy and computational constraints because of their inexpensive nature and ad-hoc method of deployment. The ability to add new functionality or perform software maintenance without having to physically reach each individual node is already an essential service. The need to reprograme a Wireless sensor networks may arise form changing application requirements, bug fixes, or during the application development cycle. A scheme is required to wirelessly reprogram the nodes. In this paper, we propose an approach to update existing code, review the requirements for building reprogramming system & compare properties and operations of some of existing network reprogramming protocols.