Find "Mobile networks"
Press the menu icon.
Press Settings.
Press Wireless & networks.
Press Mobile networks.
Activate or deactivate data connections
Press Data enabled to activate or deactivate data connections.
When the box next to the menu item is ticked (V), the function is turned on.
If you turn on the function:
Press Yes.
Press Yes.
Exit
Press the Home key to return to standby mode.