Changing form of rectangle

Hi! I am trying to do this tutorial: http://www.entheosweb.com/tutorials/coreldraw/website_design.asp, but I have a trouble at Step 3 : Creating Web Header - rather: Now go to the " Shape Tool ", double click on the bottom middle line to create a custom node / corners. I think there is a mistake in the explanation, but I don't know how to do this. Thank's for the help in advance!