To Adjust Page Width and or Height: click either the Header, Content Area or Footer then select "Property Sheet" in the upper right corner and "mktHeader", "mktContent" , or "mktFooter" should be the selected element (depending on what you selected), then adjust the width and / or height property.

TIP: include the "px" after the width/height: 300px not 300

Lorem Ipsum Dolor sit Amet (Heading 1)