ring out the old and ring in the new
1. To celebrate the end of a year and usher in the start of a new one. It's that time of year again, when companies around the city start ringing out the old and ringing in the new with raucous office parties.
2. To mark transition between two stages or phases, as one ends and another begins. The revolutionary war, which rang out the old and rang in the new for the fledgling country, also had the unintended side effect of producing tens of thousands of refugees no longer welcome in the country due to their wartime allegiance.