[SalesForce] How to re-render a lightning component when some attribute value is changed

I need to rerender a component when an attribute value is changed. I tried to put the init handler code into a helper function and called it in valueChange event handler but it did not work. Please give me some suggestions.

<!--Handler-->
<aura:handler name="change" value="{!v.dfButtonId}" action="{!c.dfButtonIdChange}"/>

<!--js controller-->
doInit: function(component, event, helper){
    //This code is working correctly
},
dfButtonIdChange:function(component, event, helper){
   //I need to rerender the component here
}