In the web application, click the 
Delete button on the toolbar.
In the desktop application:
Select the Remove item in the object's context menu.
Select the Group > Delete main menu item.
To delete selected user groups in the Groups section:
In the web application, click the Delete button on the toolbar.
In the desktop application:
Select the Remove item in the object's context menu.
Select the Group > Delete main menu item.
NOTE. To delete a user group, the user must hold the Changing User Permissions, Distributing Roles, Changing Policy privilege. When the role separation mode is active and the Deny Deleting Groups with Permissions to Access the Repository Objects checkbox is selected on the Access Control tab, the information security administrator cannot delete groups with access permissions for repository objects.
After executing one of the operations a confirmation dialog opens.
NOTE. Built-in user groups: ADMINISTRATORS and USERS cannot be deleted.
See also:
Creating User Groups and Working with Them | Viewing User and Group Objects