1. Find "Voice & Data"
Press Settings.
Press Mobile Data.
Press Mobile Data Options.
Press Voice & Data.
2. Select network mode
To turn on use of 4G primarily, press 4G.
Your phone will primarily use 4G even though it may cause an increase in battery consumption. Your phone automatically switches between 3G and 4G depending on whether you have 4G network coverage or not.
To use 3G only, press 3G.
3. Return to the home screen
Press the Home key to return to the home screen.