Access this functionality to modify groups through the menu Players (1) > Groups (2).
Locate in the group tree, the parents and children of the desired group and click on its name. When you have clicked, some options will be displayed, within these the possible operations is "Delete", as shown in this image:
To finish the process, click on "Delete"
When a group is going to be deleted and it is a parent group that has other groups within (child groups), the following will be displayed on the screen:
In this case, before finishing the process, the new group that will be the parent must be selected so that the child groups can be moved there. Then click on "Delete".