StackOverflow Answer: 38940408 v2

components.my-component.js

import Ember from 'ember';

export default Ember.Component.extend({
  actions:{
    changeAppAtComponent(){
     this.set('appName','Kumkanillam');
    }
  }
});

controllers.application.js

import Ember from 'ember';
const {computed,observer} = Ember;
export default Ember.Controller.extend({
  myService:Ember.inject.service(),
  appName: Ember.computed.alias('myService.appName'),
  actions:{
    changeApp(){
      this.set('myService.appName','NewEmberApp');
    }
  }
});

services.my-service.js

import Ember from 'ember';

export default Ember.Service.extend({
  appName:'SSS',
  changeAppName(param){
    this.set('appName',param);
  }
});

templates.application.hbs

<h1>Welcome to {{myService.appName}}</h1>
<br>
<button {{action "changeApp"}}>Change at Controller</button>
<br>
{{outlet}}
<br>
<br>
{{my-component appName=appName}}

templates.components.my-component.hbs

<button {{action "changeAppAtComponent"}}>Change at Component</button>

twiddle.json

{
  "version": "0.10.4",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.7.0",
    "ember-data": "2.7.0",
    "ember-template-compiler": "2.7.0"
  },
  "addons": {}
}