The present invention relates to a computerized method for operating changes to an irrigation system. The method includes the steps of: providing a computer processing apparatus having storage media; installing a computer program product for sizing and changing the system; loading a general database of components susceptible of being used in the system onto the storage media; loading an initial combination of components defining the configuration of the system before the change; introducing technical specifications about the final configuration of the system into the computer program product; operating one or more changes to the system in accordance with the technical specifications of the final configuration thereof. The computer program product is designed to provide a first list of components concerned by the changes and a second list containing the changes.