There are a few ways to change the thickness of a pen in Illustrator. The first way is to use the Pen tool. To change the thickness of a pen, click on the Pen tool and then drag the pen up or down. The second way is to use the Stroke tool. To change the thickness of a stroke, click on the Stroke tool and then drag it left or right. The third way is to use the Size tool. To change the thickness of a size stroke, click on the Size tool and then drag it up or down.
