There are different ways to scale a shape. The first one is using the sliders, described earlier. However, to be more precise use the white squares, located at the corners of the shape (see number 1 in the figure above), to drag the cube and change its size. Use the black squares to scale it in one direction only.
The best method is to directly input the desired length of a side, by clicking on the label, highlighted with the number 2 in the image above. These labels appear, when you hover a white square in the corner of a shape. To prevent these labels from disappearing, click on the square you are hovering with the mouse. Using the direct input method will allow you to enter the new length of a side and it’s the most precise way of resizing your shapes.