You can remove individual people one at a time, from a group, using the Group Setting screen. If you need to remove multiple people at once you can use the Group screen.
When a person is removed from a group, they will no longer have access to the group, but the messages and history will still be available to everyone else.
Step 1. If necessary, make sure you're in the Manage Organization area.
Step 2. Click the Groups panel to display all the groups in the organization.
Step 3. If necessary, you can search and select the specific group you are looking for to display all the people assigned to the group.
Step 4. Hover over the user you want to remove from the group, and click the Remove From Group option. (to complete the process and remove the user from that group.)
Remove from Group option.
Step 5. Repeat step 4 for as many people as needed.