1 Find "Network mode"
Slide your finger down the display starting from the top edge of your phone.
Press the settings icon.
Press the settings icon.
Press More settings.
Press Mobile networks.
Press Network mode.
2 Select network mode
Press GSM/WCDMA (Auto mode), GSM only or WCDMA only.
3 Return to the home screen
Press the Home key to return to the home screen.