Help How to switch 3G and 4G

[Hieu Do]

Hi folks,
I'm now using a S5 active version AT&T
Though in my country Vietnam 4G yet to available but it still show up 4G signal, anyone know how to switch to 3G cause I think 4G might be not good for battery, thanks in advance

 

[Jfalls63]

http://www.droidiser.com/2014/05/force-enable-3g-android-phone.html?m=1

Found this and checked it out on my phone and was able to enter the options menu. I didn't try to change mine.