Step 1: take a section cut (of the desired section render)
Step 2: Select everything EXCEPT THE section cut plane
Step 3: Hide the desired section cut (what is selected)
Step 4: Go to "View" and deselect Section cut and Section plane if not already deselected
Step 5: After having done this, the other portion of your model will appear (the undesired section cut)
Step 6: Select all and DELETE
Step 7: Go to "Edit" and select Unhide --> All
Step 8: Then RENDER
Step 9: after having rendered, make sure to undo the delete of the undesired section cut so it is not gone

Hope this helps...