A remote upgrade server having a networking module and a processing unit is provided. The networking module provides a network access service. The processing unit receives an update checking request from a mobile communication device via the networking module, and determines a delay time period according to a current networking load in response to the update checking request. Also, the processing unit transmits an update configuration file including the delay time period to the mobile communication device via the networking module, so that the mobile communication device downloads the system update file from the remote upgrade server after the delay time period.