You can resize any object by clicking and dragging the black selection handles around it. Learn how in this article.
An alternate way to re-size an object is to select the object then type desired dimensions into the Width and Height fields on the Design tab.
The final way to re-size an object is by selecting the object then clicking on the dimension and typing the desired dimension using your keyboard. Press Enter from your keyboard or click elsewhere in your Work Area to save the typed dimension.