Which extenders are you referring to? The ball and socket joints that resemble barbells? If not, dipping the parts in boiling water usually softens and loosens up the parts enough to take them apart without breaking them (as long as they're not screwed together, etc.).
Not sure what they are called but the seperate part that is at the end of the ankle to make the figure taller and is the socket where the pegs plug into. Not sure if these are permanently fixed or can pop out with a bit of heat.