code: function(oldModel, newModel){
          var index;
  
          if (oldModel && newModel && this.hasModel(oldModel) && !this.hasModel(newModel)) {
              index = this.indexOf(oldModel);
  
              if (index > -1) {
                  this.act(function(){
                      this.add(newModel, index);
  
                      this.remove(oldModel);
                  });
  
                  !this.isActive() && this.signalChange() && this.resetChange();
              }
          }
  
          return this;
      }
docs: Replace an existing model with a new one
  @param  {Class} oldModel A Model instance that will be replaced with the new
  @param  {Object || Class} newModel An object or Model instance that will replace the old
  @return {Class} Collection Instance