NGUI sprite size

Hi, I have a problem with ngui sprite. After I click the button - sprite1 changes to the sprite2. Then I click again and sprite2 changes to sprite3 and so on. It works, but sprite2 comes lower, it’s picture size becomes bigger (however, no changes in transform are shown). In fact, I can’t even properly say what exactly changes. How can I prevent it?
before:

after:

Like @Simon Larsen said, both images have different size but you are showing in same size, so it need to be scaled. In atlas object you can manipulate sprite size, border, etc.

For a better GUI you should use texture images in same size in pixel that you will render. Sprites have MakePixelPerfect() method that rescale its object to correct size when you change it.