This option lets you delete or add any  of  nine  types  of  planet,  orbiting 
stars, asteroid belts, gas clouds, and ring-worlds.
  To select press the planet number, 1 to 9 (or A to H for planets 10 to 17)
eg;
       Key  1  2  3  4  5  6  7  8  9  A   B   C   D   E   F   G   H
     Orbit  1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17
The best way to position planets is to generate a solar system. For ringworlds 
it's essential to put the ring at a distance that will  support  the  type  of 
atmosphere  you  want.  Do  this by replacing an axygen world (or toxic world) 
with the ring.  There are good reasons to assume that there won't be any other 
astronomical  objects in a ringworld system,  apart from a single well-behaved 
star and possibly distant gas clouds, so edit them out.