Load your figure. Select its body. Look over the parameter dials for Scale. Default is set at 100%. You may increase or decrease that scale. You can scale specific parts. You can make legs shorter by setting YScale on the thighs and shins down to 90%, for example. Make them longer by going up to a YScale up to 110%. Just changing the YScale will either make them shorter but thicker, or longer but leaner (relatively speaking). Increasing the XScale on the torso a little bit can have the visual effect of adding pounds. Decreasing the YScale does the same thing, and makes the person shorter. For anything more, you need to use morph targets (downloaded or bought), or make your own in Poser using magnets.