Samsung Galaxy S5 - android 5.1.1. 4G/LTE problem

Hello, I would like to find out when is AT&T planning on issue android 6 Marshmallow for Samsung Galaxy s5? After last couple of updates I have a problem with my mobile Internet. It runs on E(edge) even though the area is covered with LTE amd every other device has LTE as well. What can I do about it? Every other carrier has issued android 6 update