A function update method improving household appliance functions by enabling new and existing household appliances to perform cooperative processing. In the method, a server stores registration information listing identification information for each household appliance owned by a user, combination information listing combinations each including household appliances performing cooperative processing, and update information for each household appliance in each combination, for updating a function for performing the cooperative processing. The method includes: receiving, from a household appliance having identification information not listed in the registration information, a request to list the identification information in the registration information, and listing the identification information in the registration information; selecting a combination listed in the combination information, the combination including the household appliance and all other household appliances in the combination being registered in the registration information; and transmitting update information to each household appliance requiring a function update in the combination.