The torso is likely two separate pieces of hard plastic glued together, so the heating method won't work. I remember there's a tip in the tutorial section about drilling a small hole along the seam of the torso (which can be filled in with sculpting material after reassembly), then using a small flathead screwdriver to pry it apart. I've done this a few times with varying success, most of the time it works and the it's salvageable, but 2 or 3 times the pieces have been so tightly glued together I was unable to get the arms removed without destroying the torso.