There are three kinds of changes you may be faced with at some point as a manager or supervisor:

The first is needing to reduce the size of your department because of poor company results, or a strategic redirection such as merging with another company or divesting an activity.  In this case you should maintain an ongoing dialog with employees on company results and targets.  Focus on individual and team goals.  As long as these goals are clear and employees get regular feedback, personnel changes will not be as surprising and individuals will know their own value.  You may find that certain individuals decide to leave on their own during this period because they see the risk and don't want to wait for something to happen.  There is nothing you can do about that, but just know that you are doing the right thing by keeping your employees informed.  There may be times for confidential reasons you can't tell them what is going on in advance...that is a reality as well, but do not let them find out information in a memo.  Right before any information is sent out, fill your employees in.

The second kind of personnel change you may be faced with is having to let somebody go because of performance issues.  This can be difficult on others in your department.  Maybe the person you let go was friends with other employees; they could be upset with you and disgruntled because of the change.  Or the remaining employees may be upset because of additional workload they need to take on without the other person there.  Once again you need to be honest with your employees.  Talk about expectations for the job.  Be consistent in how you set and follow-up on expectations for each of your employees.  It should not be a shock to anyone when a poor performer gets let go.  What you have in your control is how you manage it afterward.  Make sure the workload does not fall on one individual.  Recognize the efforts of others on your team when they step in and fill the gaps.  Make sure to fill the open position quickly and ask your existing employees to help with the hiring choice.  This will help get them to support the new employee once they come on board.  

The third kind of personnel change you may be faced with is hiring and integrating a new employee into the team.  This often brings up jealousy from the rest of the group.  Make sure the process flows of you team are clear and workload is defined.  You want your team to embrace a new individual, see the value they bring to the group and help them to achieve success. Once again, by bringing your current employees into the hiring process for new team members, they have a vested interest in the new employee's success.

Read the following blog post for more information on interviewing candidates and involving your current team in the process. Interview tactics for the InterviewER