Go to the Admin Menu → allGroups
Select a group name you want to remove the user from.
Go to the Membership Roster list at bottom of the screen.

Click the Remove User button
next to the name of person in the list you want to remove from that group.
Tip: If it is a long list of members, you can search for the persons name first
Note: BE SURE THIS IS THE PERSON YOU WANT TO REMOVE BY CHECKING THE EMAIL ADDRESS. SOMETIMES PEOPLE CAN HAVE THE SAME NAME.