I'm not sure I understand your question, but here are some guidelines when changing the IP address.
There are two places that will need to be changed, and you will need to change them in the correct order. Let's assume the IP address of the PLC is currently 192.168.0.1 and you are successfully communicating with it. To change the PLC's IP address you must first open the hardware configure for the PLC and change the IP address for the appropriate port, typically either the Ethernet port on the CPU module or the port on the ETM module. After making the change in hardware configuration you must download the changed configuration to the PLC. You must stop the PLC before you can download configuration changes. If you don't stop the PLC you aren't given the option to download the new configuration.
After you download the configuration with the changed IP address you will lose communication with the PLC. To reestablish communications you will need to look at the properties window of the PLC target and change the IP address there. That is where you set the method that Proficy Machine Edition will use to communicate with the PLC, either serial or Ethernet and the IP address of the of the target if using ethernet. Once you have changed the IP address that Proficy Machine Edition uses for communications you will be able to get back online with the PLC.