This is a great question. Most importantly, each situation will be different. So, everything needs to be tailored to the context. However, there are a few point that will help.
First, it will be important for the administrator to get all the teachers apprised of the new change. For this to happen, the administrator should give ample time for teachers to know the time of change. The administrator should also plan time for teachers to ask questions and voice their opinions.
Second, teachers should buy into this new change and start letting students and parents know. The administrator should make sure that this is happening. New changes can be tricky. More information is best.
Finally, the administrator should also make sure that all the materials are ready for the new reading program.