Resizing the Image

Note in the titlebar that it has a "50%" indicator. This indicates that the image is much larger than it appears (twice the size). This tells me that the image is bigger than I want it to be, so I'll scale the image down. Right-click on the image, and select "Image -> Scale Image ..." I've chosen to reduce the image to 75% of its original size:

Notice that by default the ratios are locked (or "chained") together: when I change one, the other follows. This is usually what you want so the proportions of the image remain the same. The resized image appears smaller, as you might expect. To work with it at 1:1 (100%), right-click on the image, choose "View -> Zoom -> 1:1". You'll notice that there's a number "1" after "1:1" on the menu - this indicates that you can do the same thing by pressing the "1" key.

Now we have another problem: we can't see the whole image. The window we're working in stayed the same size while the image inside it doubled in size, so now we have scroll bars along each side of the image. Scroll bars are a good way to move around a large image (or one you have at high magnification to see the details), but in this case it would be nice to see the whole image in one window without scrolling.

Right-click on the image, select "View -> Shrink Wrap" and you'll have the whole image available to you (if it will fit on your screen).