Access this functionality to modify groups through the menu Players (1) > Groups (2).
In the group tree, locate the parents and children of the desired group and click on its name. When you have clicked, some options will be shown, within these the possible operations is "Update" (3), as shown in this image:
In this window it will be possible to modify the name of the group, if this would be the default group when creating a new player in addition to modifying the parent group to which it belongs.
Complete the fields and click the Update button.