In Illustrator, you can change the document size by using the Size property. To change the document size in Illustrator, follow these steps:

  1. In the File menu, choose New > Document.
  2. In the New Document dialog box, enter a name for your new document and click OK.
  3. The new document will be created with a default size of 100% of the screen width and height. To change this size, use the Size property to change it to a different value. For example, if you want your new document to be twice as wide or twice as high as its original size, use the Size property to set it to 200% or 400%.