Default [Q] How To enable other LTE bands AT&T GS4

hello people,
i would like to enable LTE band 4 or any other faster band on my phone i am currently on LTE band 14. i i would like to switch to make it faster for all around use i know i have all the att bands in my area because i live in dallas ATT's HQ and i have looked it up.
things i have tried
1. using 4636 and then select band and nothing pops up to switch to it says (set GSM/UMTS band) thats it
2. i have flashed a differnt modem didnt work or im not doing something right
thats all i have looked it up and have followed the guides and they dont work
i was going to try to enable a T-Mobile AWS guide but i think you have to have a T-Mobile sim but idk
if you cant help that fine if you can thaks a lot
IF SOMEONE HAS SOLVED THIS ALREADY SORRY FOR NOT FOLLOWING THE RULES I JUST CANT SEEM TO FIND TO RIGHT FIX/GUIDE
thanks,
DyslexicTurtle