Q: how can i use less data on Iphone 6? I already turned on the wifi setting.

Hi DJAgent,

Welcome to the Apple Support Communities!

I understand that you would like information on limiting data usage on your iPhone 6. There are a couple of different resources I would recommend you read over in this situation. First, I suggest reading over the first article that explains how you can view and adjust data usage for specific applications and monitor usage. 

Learn about cellular data settings and usage on your iPhone and iPad (Cellular Model) - Apple Support

Another area you may consider looking at is Location Services. I would suggest reading over the information on Location Services and deciding what applications need to be using your location. 

Understanding privacy and Location Services on iPhone, iPad, and iPod touch with iOS 8 - Apple Support

Best regards,

Joe