A program-changing method for a network having at least two nodes that include a first and a second predetermined node, each network node having a program, includes a network management system connected to the first predetermined node of the network. New changing program data and a control signal are transmitted to the first predetermined node connected to the network management system which is disposed in the network separately from the nodes and configured to manage the changing of the programs in the nodes. The first predetermined node replaces its program with the new changing program data. The network management system transmits a program-transmitting-signal to the first predetermined node, causing the transmission of the newly changed program data stored therein to the next predetermined node to change the program of the next predetermined node under control of a respective control signal to the second predetermined node from the network management system.