(HELP) LTE Frequency change

Hello friends I have a Samsung Galaxy S5 900a at&t which does not grab me lte neither H, only E

my operator has the following configuration:

GSM/GPRS/EDGE 900/1800Mhz, 3G/HSPA+ 900Mhz y 4G/LTE 1800Mhz

as I can do to have 4g?
I can turn my phone on 900h?