In the menu Tools → Modify Parts, you'll find the Delete parts under elements function, which allows you to remove parts located beneath selected elements. You can also use the
button on the CAD toolbar for this purpose.
If you have already selected the elements before activating the function, the parts under the selected elements will be deleted immediately. If no elements have been selected in advance, a dialog box will open where you can select the relevant elements. The parts underneath them will then be deleted.