Click the control to be sized. Sizing handles appear (usually 8, at the corners and the middle of each edge of the control). Each handle will let you move the relevant edge or corner.
Drag the handle you want to move: as you size the control the status bar will be updated with the new size. The size will change in jumps if you have Snap to Grid enabled.
Release the mouse button to complete the operation, or press <Esc> to cancel.
You can also size most controls by setting the size in the General Page of the control's properties.
You can size a map in exactly the same way as you size other controls. The sizing handles for a map are displayed permanently. Only the parts of the handles that are inside the map are visible.