Define switched?
Do you mean
inverted?: Pressing the pedal reduces braking/acceleration, releasing the pedal applies pressure to the brakes/accelerator.
Do you mean
swapped?: Pressing the brake presses the accelerator and vice-versa.
If you mean
inverted:
Try clicking the invert button in LFS > Options > Controls > Axes/FF next to the brake and accelerator.
If you mean
swapped:
You need to assign the brake and accelerator to the correct axis. You can do this in LFS > Options > Controls > Axes/FF. Click the accelerator button on the left, then press the accelerator pedal. Click the axis that moved. Do the same for the brake pedal.