Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
The option is only available if you have a content blocker actually installed as far as I'm aware.
 
Settings-->Safari-->content blockers.

You have to download them from the App Store. They'll be available when iOS 9 goes live.
that option is not there for me. i gues sfirst i have to install the app
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.