To remove polygons that are
not needed for the analysis
do any of the following:

1. Use Edit->Clip to remove
all but an area within your
circuit. You may wish turn
off snap to grid before you
clip using Tools->Snap Setup
and its "No Snap" radio button. 

2. Use the mouse to select
polygons and delete them.

3. Use the Circuit->Dielectric
Levels and its "Delete" button
to remove unneeded levels.
