How to change/stretch the viewport dimension/shape?

Hi guys

How to change/stretch the viewport dimension/shape?

Sometimes I create a viewport; than when I set the scale in the viewport, the viewport isn't big enought to contain the drawing. In AtuoCAD I can change the dimension/shape of the viewports by click on the viewport's border and stretch the shape using the corners like a simply rectangular.

Many thanks in advance.

Antonio