"To change the manager" means to replace or switch the person who is in charge, responsible for making decisions, and leading a team or organization. Full definition
If we don't change our manager at the end of this season, it is not beyond the realms of possibility that we could get relegated next season. (justarsenal.com)
Teams which haven't changed their manager in a few years right? (justarsenal.com)
Throughout the observation period, about half of the employees changed managers at least once, and the researchers focused specifically on employees who switched to working for a manager of a different gender. (businessinsider.com)