Against each existing goal on the Enterprise Goals panel, you will find an Archive button. An archived goal cannot be used as an object on a benefits map. Click on Delete below the archived goal to permanently delete it. After this, the goal cannot be restored again.
Click on the Archive filter in the top right corner of your goals list to show the goals that have been sent to the archive. Click on the Restore button below the archived goal to restore the goal to the non-archived list of goals. Click on Delete underneath the archived goal to permanently delete it. A goal that has been deleted cannot be restored.