Click Manage Groups in the bottom left corner
Click Pencil next to the group you'd like to delete
Click red trashcan icon
Read through the implications of deleting that specific group. If you approve then type the name of the group to confirm deletion.
Click Delete Group
Deleting a group removes all the updates and task from that group. Deleting a group removes it from the entire organization and not just your account.
Deleting a group cannot be undone.