The selection tool will now resize the image to fit in one screen. You also can calculate size changes using subtraction, addition and division, represented by a hyphen, plus sign and forward slash, respectively. In the tool properties, click on the resample button. To enter percentages instead of dimensions, type an asterisk to indicate multiplication, followed by a number representing the scaling factor as a value less than 1 for reductions and larger than 1 for enlargements. You also can type in new measurements for both width and height, using the 'Tab' key to move from width to height or 'Shift-Tab' to move from height to width.

Add the 'Alt' key to the combination and the scaling process applies to a duplicate of the selection. When you hold down the 'Ctrl' key while you press 'Enter,' the result scales proportionately instead. If you select and replace one of the current dimensions and press the 'Enter' key to commit your change, the result scales disproportionately. Use Adobe Illustrator's Transform panel to scale objects when you know either the width or the height of your target size, expressed dimensionally or as a percentage.

How to resize an image on illustrator