There are instances where a member or an individual is no longer a part of a group.
To understand how to remove a user in a group, you must know all the roles available. They are defined here
To remove someone, you can either "block" them or select them in the Manage Memberships section and on the "Action" column, remove their roles.
Note: If the individual has registered, they will be designated Registrant, if they volunteered or added an impact, they will be designated with a role Participant. Individuals and users who have these roles may not permanently be removed from your group. To delete and completely purge them from your database, please contact firstname.lastname@example.org
Reason for now removing users with Registrant or Participant roles: This is b/c we believe these users may in the future become a member again, and this will give you a better idea of collecting information about them. This also works well for instances where you block people from joining your group and seeing your private events by ensuring they apply to be a member.
For more information on setting up applications or requiring users to provide you information before they can be a member you can review this: Manage Memberships Application Management