Removing and replacing 25th arms and heads?

I'm sure it's already been asked here, but I can't find it anywhere. What's the best way to remove and replace 25th arms and heads? I don't want to use the rubber mallet approach, but I can't think of another way.

Well the heads just pop right off - so no magic to that. No hot water needed or anything, just tug.

The arms, you need to split the torso to get it to work, because of the way they're placed inside the chest. Lower arms you should be able to "boil-n-pop" to remove/replace, but upper arms require splitting the torso apart.