gistfile1.js

i = 0;
 print("View load: " + db["Views." + x].find({ created_at:{ $exists:true}}).count());
  db["Views." + x].find({ created_at:{ $exists:true}}).forEach(function(y){ 
    y.timestamp = y.created_at;
    delete y['created_at'];
   db["Views." + x].save(y);
});

//OR:
  db["Views." + x].remove({ created_at:{ $exists:true}});