Animation question

Hi I have a problem with the animation of my character, my character when it still has a size of 30x62 (the prototype), the images of my character when it is still measuring 30x62, but the animation for when you are dying or walking are a different size, when my character the actor is doing great and small, say that the animation is changing the size of 30x62 to 34x64, must have all images the same size? would not be correct because when walking the collision is different, as my character when it is bent, measures 30x44 is horrible the animation of walking, is big, small, big, small .... I am doing wrong? I can do all the images to 30x62 but then collisions would never correct ....