You can change the number of generations to be printed by using the scroll menus at the bottom of the screen. You can then change the person the tree is centered on by selecting different people.
I find it helpful to select the oldest child of the youngest generation that is entirely on the side of the family you want to print, eg they are in a relationship with a member of the generation you don't want to print), and then add or remove cousins with the 'Other' menu. (I hope that all makes sense!)
Hope this helps!