Here's how to enable and/or disable 4G data services on your Nokia Lumia 820:
- From the Start screen, swipe to the left.
- Scroll down to and tap Settings.
- Scroll down to and tap mobile network.
- Tap the Highest connection speed field.
- Tap 3G.
- The 4G connection has been disabled.
That's it - the 4G connection for your Nokia Lumia 820 has been disabled.