A group's Founder and group Admin(s) have the ability to ban members from the group. There are two ways to ban a member from a group.
To ban a member from your group via the "Members" page:
Navigate to the group's main page.
Click on the "Members" link, located below the group's cover photo.
Click on the orange "Edit Members" button.
Locate the member You wish to promote.
Click the orange "Ban" button, located beneath the member's username and avatar.
To ban a member from your group when viewing a discussion post:
Navigate to a discussion post which was posted by the member you are going to ban, or contains a reply by the member you are going to ban.
Click on the downward shaped triangle (located to the right of the chat bubble and heart icons).
Choose "Ban" from the drop-down menu.