I saw some instructions the other day about swapping the biceps on leader Prime as they were factory swapped. The sculpted details should be on the outside of the arm. The instructions I saw involved taking apart the upper arm, which involves breaking glue that holds the part together and a lot of timy parts. Well, there's an easier way to do this that doesn't involve breaking any glue. To note is thay there are 2 sized of screws involved, keep them sorted. The threadings are different. Watch for the springs and such inside the joint. First, open the shoulder casings. 2 screws each. Be sure not to lose the small metal rod that keeps the blue flap on. Set pieces aside. Now, open the forearms. Remove the gun and set the arms flat, removing the 3 screws. The elbow screws are large, the wrist and back screws smaller. Carefully open the arm, watch for the springs and such inside the joint. The small blue detail bit on the top of the forearm is also a separate piece, keep an eye on it. Good. Now the 2 bicep bits are free. Rotate the elbow cylinder around, swap them to the opposite forearms. Manually rotate the small black bit in each elbow joint so the notch lines up- it should face backward now. Press the bicep down over the spring and reassemble the forearm. Then reassemble the shoulders.