Dear Rosie,
Whilst change is an inevitable part of life, people by nature are inclined to resist change when it happens. Change management therefore is always a challenging task. During times of change, CEO’s role is to be Chief Communicator and Project Manager of change management to assure smooth implementation of change. I think the best way for CEO to manager change is to first communicate with company’s leadership team about why change is necessary to gain their consensus, e.g. to increase business efficiency, to keep company remained competitive. Once consensus of leadership team is gained, the communication must be cascaded to next levels. Depends on situations, the communication can be from this leadership team to their direct reports, or CEO can hold a “town hall” meeting to communicate to all employees. The next thing is to develop a “game plan” and then to execute that plan to implement change.

I hope the above can address your first scenario. Regarding the 2nd scenario - I am the new CEO to a firm, I certainly will first introduce myslelf to leadership team, and then to the whole company, where I show my commitment to transform the firm and ask for my colleagues' supports.