When you say it's in Auto, I am assuming you are not meaning the Green square Auto mode? You won't have any control over the AF in that mode.
In AV, TV, M mode, you should be able to switch between the modes by pressing the AF button on the top, back right of your camera body, and then immediately pressing the small, m.Fn button above the shutter, which should cycle you through the different AF areas. You can choose with button or control to use for switching between the modes, in Autofocus menu AF4, AF Area Selection Method. Go into that option and choose whether to use the M.Fn button or the Main Dial.
Hope that helps
On my 7D I changed it from the quick menu, and here I never bothered to change it and now when I wanted I couldn't make it work. Anyway thank you!