Systems and methods for performing a software upgrade for a first offline charging system (OFCS) having a plurality of virtual machines implementing charging functions for offline charging. For the upgrade, a controller identifies a subset of the virtual machines in the first OFCS to remove from service, transmits a request to a distributor to reduce the distribution of the accounting requests in proportion to the number of the virtual machines removed from service, and removes the subset of virtual machines from service in the first OFCS. The controller also constructs updated virtual machines having the software upgrade in a second OFCS to replace the virtual machines removed from the first OFCS, and transmits a request to the distributor to increase distribution of the accounting requests to the second OFCS in proportion to the number of the updated virtual machines constructed in the second OFCS.