There are some occasions where you may want to remove old members in order to make room for new members - for example if a class of students leaves and you want to use the account licences for other students.
To remove members:
Click your name/gravatar, bottom of the left hand pane
Click on the name of your educational organization - under My Organizations, which is about halfway down the screen.
Click the Members tab
Under Permanent Teams, Click All Members
You will be able to see all the members of your school organization.
Choose Remove on the right hand side of the name of the person who you want to remove from your organization.
If you want to use the freed-up accounts with new students, follow the steps listed in Add Users