Re: can i go from 3g to 4g?
The difference between a phone that can only do 3G and one that can also do 4G is in the hardware, and it would cost more to have someone design a motherboard for your phone that can do 4G than it would take to buy everything in a Best Buy store just before they opened on Black Friday. (IOW, about as much as it costs to design a new cellphone.)
The only way to "go from" 3G to 4G is to buy a phone that can do 4G. (Or do your data downloads on wifi - that's usually faster.)