Once you have created a group there are a number of changes you can make to it, including editing the group name, deleting the group, and adding or removing users.
If you click Groups under Team, you will be able to see all groups and the child groups under them.
Clicking on the button on the right will give you a few options. You can change the name of the Group, move, duplicate, or delete a group as well as auto-subsribe a Group to a Topic and make a Group a default Group for new users.
Clicking on Create New Group will let you create a group anywhere in the hierarchy.
You can only delete a group after you have removed all users and archived all posts under it.