iPhone 6S Hard Reset Using iTune Software

In the Left menu in iTunes Select your phone.
Press Restore button in iTunes.
Remember! Here you can take backup of your data if you want.
Then click Restore to confirm information about this procedure.
Now your iTunes will download, prepare and restore the software on your iPhone.
To finish operation choose "Set up as a new iPhone".
Enter a name for your phone.
Great! You have performed Hard Reset Process!