Find "Mobile networks"
Slide two fingers down the display starting from the top edge of your phone.
Press Settings.
Press Settings.
Press More....
Press Mobile networks.
Turn data roaming on or off
Press Data roaming to turn the function on or off.
If you turn on data roaming:
Press OK to confirm.
Press OK to confirm.
Return to the home screen
Press the home icon to return to the home screen.