1. A communication terminal including a rewritable non-volatile memory and a rewritable volatile memory, the communication terminal comprising: means for limiting operation of software using the rewritable volatile memory in response to a received update file information and securing, in response to the received update file information, an area required for storing the update file in the rewritable volatile memory before receiving the update file from a software management server, the volatile memory being used by the software during normal operation; means for requesting transfer of the update file to the software management server after the area required for storing the update file in the rewritable volatile memory is secured; means for receiving the update file from the software management server, and storing the update file in the rewritable volatile memory; and means for rewriting software stored in the rewritable non-volatile memory that is directly executed, with the update file stored in the rewritable volatile memory.