WWW.progress not working unityWEB

WWW.progress not working on web when load asset bundles first time.It always show 1 or 0.
It works fine when asset load from cache memory.

As given in below link i have to add header file in server.
http://answers.unity3d.com/questions/594668/wwwprogress-not-working-on-android-ios-1.html
But any one please tell me where should i have write this code ??
I don't know much about server side coding. Please explain me step by step .