Step 1

When you select an object, a bounding box will appear around the the object. These are the blue lines + the little boxes on the corners.

Step 2

By selecting on the boxes in the corners and dragging it you can change the size of the object.

Step 3

By selecting a side and dragging it, you can expand the object in that direction.

Step 4

When you drag and hold "Shift" the resize will stay in the same proportions.

Step 5

And when you hold "alt" while dragging the other side will be adjusted in the same way.