Select the line, choose the pencil tool, click one of the nodes at the end of
the segment you want to change, hold the left mouse button down and drage.
If you want to collapse the segment, once a single node has been identified,
hit the delete key.
You can also do as Paul suggested, if you have both the drawing window open
and the shapesheet open, tile them so you can see both. Then as you click a
geometry entry, the corresponding node in the drawing window will highlight
(black square). Hunt for the nodes you want to delete, then delete the row
in the shapesheet.
Either way works.
Wapperdude