If only I knew what exacly you were talking about.. I can only help in two ways though, 'cause I think I know what you mean..
If your hoping to resize the whole thing then just pull on those blue boxes at the corners and sides of the thing.. If your talking about when you zoom in with the magnifying glass then I would try using the MG thing again and it'll go back to normal.
A more precise way to do it is by clicking on Image, then Attributes, and then changing the number for each dimension (measured in pixels, centimeters, or inches, your choice).