You can manage the layouts that are available through either the Layout Manager or Preset Manager depending on what other versions of tools you have installed, they are just different names for the manager.
In here you should be able to select SiteAssist Pro and manage the layouts available. You should be able to find more layouts for the default designs in your download history. I'm not sure if what you are experiencing is a problem with the layouts or some other issue in the tool. If you can please post back with some screen shots of what you are experiencing so that we have a reference.