• In a directory you place the level extractor program : (ltextr.exe),
  and the levels file from which you want to extract levels (LaserTank.lvl, temp.lvl, kids.lvl or any other levels files).
   
• Then you open a "DOS" session and from there you type this: ltextr LaserTank.lvl 4-17 result.lvl
  or ltextr temp.lvl 4-17 result.lvl or  ltextr kids.lvl 4-17 result.lvl 
   
• You now have a new level file named result.lvl which contain the levels 4 to 17 from the LaserTank.lvl file,
  or from the temp.lvl file or from the kids.lvl file.
   
• If you typed ltextr LaserTank.lvl 15 result.lvl  instead, the result will contain only the level 15.

That's it.

Donald