How to get all game objects and remove some of them..

So I'm going to assume you don't have a list or array of the objects named numerically.

So first, find all objects tagged with Boss : http://docs.unity3d.com/Documentation/ScriptReference/GameObject.FindGameObjectsWithTag.html

Then loop through all the returned gameObjects, convert the name to an integer, then check if it is less than 8 :

 for ( var go : GameObject in returnedObjects )
 {
     // convert name to integer
     var nameInt : int = parseInt( go.name );
     
     // check if it is less than 8
     if ( nameInt < 8 )
     {
         // remove object
     }
 }