Updated for 7.0
On the left-hand side of the screen in the navigation bar under Member, select Group(s). This will take you here:
In the table titled List, scroll to find the group you want to edit. This will take you here:
Click the name of the group to begin editing.
In the menu bar at the top of the screen, select Members. This will take you here:
Scroll to find the name of the member you want to remove.
To remove a member, select the red button with a trash can icon to the far right of the screen in the same row as their name.