To change those railings, the easiest way is to edit the existing segments. To to this:
1. Open the Style Editor
and find and selectthe Segment called allum_rail_01
wired in the Default
2. Click the Extract button
to add the segment's geometry to your scene.
3. Edit the geometry to remove the elements you don't need.
I hope that helps, please let me know if you have any further questions.