Using Autonomous Selector
Without SD Card
With a competition switch, run your code in disable. Select the autonomous on the screen by pressing the left / right buttons until you're on the page you want. Run the autonomous!
With SD Card
The last page you're on will save to the SD Card. So if you're running Page 3, select it once using the steps above, then you won't have to select it again.
To use an SD Card with the brain, just plug it in and EZ-Template will generate the files needed.