Complete the game, then go back to the first area in the game (Blackfoot Territory). Locate the higher boulder that leads up to a ledge and a gap. While on a horse at the left side of that boulder, jump and use your spurs until you land on top of the boulder. After that, get onto the ledge. Ride across the next two areas. Then stop between the two rocks in the water. Hold V + SHIFT + C + SPACE + LEFT MOUSE BUTTON until the confirmation sound is played. Enter the options screen and a new option named "Gun" will appear. Once selected, you can replay any main mission or side mission (from checkpoints if desired), view the intermission sequences, and toggle the help messages. Note: You will have your current weapons, items, and skills when a mission is replayed.