In an image forming system which has a client unit, a management unit, and a printer unit, when the client unit issues a replacement print request to the management unit, the management unit notifies the client unit of the contents of the print queue in response to the replacement print request. The client unit displays the notified contents of the print queue, and prompts the user to designate a print job to be replaced and an inserting position of a new print job into the print queue. After that, the client unit outputs, to the management unit, replacement information which includes information indicating the designated print job to be replaced, information indicating the designated inserting position, and the new print job. The management unit updates the print queue in accordance with this replacement information.