The dial's turning direction for setting the shutter speed and aperture can be reversed by following these steps:

1. Power the camera on.
2. Press the <MENU> button.
3. Select the [Custom Functions] tab.
4. Select [Custom Function Group IV].
5. Press the <SET> button.
6. Select [C.Fn. IV-4: Dial Direction During TV/Av].
7. Press the <SET> button.
8. Select [1: Reverse Direction].
9. Press the <SET> button.

In the manual mode, the direction of the adjustment dial and the quick control dial will be reversed. In other shooting modes, the adjustment dial will be reversed. The direction of the quick control dial will be the same in the manual mode and for setting exposure compensation.

A reference to this can be found on page 183 of the camera user guide.