Requirement: To remove group members from an existing group, you must be the admin of this group.

Go to “My Groups” using the drop-down menu in the top right header bar. Select the desired group from the group overview here.

At this point you should be able to view the group's member list.
There are three dots next to each name on the right side. If you click on this, you can use the “Remove from group” option to remove the member from the group.