Loosen the lever attachment to the door by rotating any screws that hold it together. Use a screwdriver or a drill to remove these screws and set them aside to use later. Remove the portion of the latch that sticks out the edge of the door by twisting it in place until it comes out or by unscrewing another attachment point possibly contained within the interior lever assembly and visible only after the external levers are removed.
Take the various lever pieces out of the door. Rotate the lever setup and hold it against the door so that it is upside down and backwards. Check to see if any additional portions of the door need to be drilled or enlarged to allow the lever to fit in with this orientation. Make any necessary adjustments.
Set the internal latch portion within the door and slide the edge latch piece back into place. Rotate it to attach it, or secure it with the internal screw that was removed earlier. Reinstall any external sections or door levers that you removed earlier, using the original hardware and a screwdriver or drill.
Test the door by closing and opening it. Make any necessary adjustments if there is a problem with the fit of the door lever mechanism in the door frame.