In the present era, rapid boost of technology has created a lot of confusion for the usage of correct technology and for the correct purpose. Mobile telecommunication technology is one such field in which usage of correct technology can enhance the performance of your Android device to many folds. For example, if you use 3G or 4G technology for the communication, the difference may be enormous. But, the major problem is the availability of the technology in the area of working. For example, if you are working in an area where only 2G communication is available, you cannot avail the 3G or 4G, despite the fact that your Android has the option to use 3G or 4G technologies.
Android has resolved this issue by offering a feature which, when activated, can automatically, convert to the highest level of technology. For example, if you move from the area where your Android device is using 2G, and move to the area where higher generation of telecommunication facility is available, your Android device will automatically start to use 3G or 4G, which ever is available. In the situation you do not need to switch over to the 3G or back to 2G, which ever may be the situation of availability of appropriate level of technology.
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You may enable this feature, easily, but if you feel any problem, do not hesitate to see the instructions.
Instructions
1: Tap the icon of the ‘Settings’ at the Home screen of your Android 5.0.2 Lollipop device to open up the ‘Settings’ screen.
2: At the ‘Settings’ screen, tap the ‘Data usage, in ‘Wireless & networks’ section.
3: At the ‘Data usage’ screen, tap the settings button, placed at the top right corner of the screen, immediately below the status bar. It will open up a popup menu.
4: Tap the ‘Cellular networks’ in the popup menu.
5: At the ‘Cellular network settings’ screen, see the current status of the ‘Preferred network type’ is ‘2G’. If you want to change the status, tap it. It will open up a prompt. 
6: At the prompt, see, current status of the ‘Preferred network type’ is ‘2G’.
7: Tap ‘3G’ if you want to change the type. It will instantly take you back to the ‘Cellular network settings’ screen where the status is change to ‘3G’. 
That’s all!