Heres a little trick to access download booster on galaxys5 at&t
The directions are for Nova Launcher but will work for Apex Launcher and others. After installing Nova Launcher, open the app up and long-press on your Galaxy S5's home screen, choose Shortcuts, tap Activities, tap Settings, then tap Download Booster. You'll now be able to toggle Download Booster on and off.
And yes it works you do get the option in settings does it actually improve download speeds? Well you will have to be the judge of that.
Posted from galaxyS5