Change management $$ there are different methodologies used to change from a current system to another, taking into account the complexity and importance of the current $$old$$ system:

Two options, aside from cutting off and starting the new system right away, or running both old and new at the same time, is the $\_\_\_\_\_\_\_\_\_\_\_\_\_\_$ option, where a subset of the organization is the first to use the new system. The $\_\_\_\_\_\_\_\_\_\_\_\_\_$ option is used when only some functions are switched to the new system, followed by addition of other functions until the system is complete.