While on your home screen, "pinch" it using your thumb and forefinger. This should bring up a screen showing all your home screens, or panels.
At the bottom of each panel you'll see a little house icon; the green one shows your "main" home screen. To change it, just tap the house icon of the screen you want to be your "main" home screen.
By the way, from the screen showing all the panels, you can jump to any panel by just touching it.
You can also set the preferences to jump to that screen with all the panels by swiping up (in addition to pinching), and to jump to your main home panel from any other panel by just swiping down.