The instructions in the read me really only cover importing the layout into the layout manager. Inside of texture all is the texture100.zip and TextureHomePage100.zip. These are the files that you import into your CSS Sculptor Layout Manager.
To update the images you would need to edit the source files, you could then save your edited image files into the presets for texture for the various color schemes. This way you could just import the layout and have it include your edited images.
Once you have the layouts available to you in the CSS Sculptor Layout Manager you can then use these layouts to create a new SiteAssist Pro design. On the SiteAssist Pro support page under How To there is a document that explains how to create new SiteAssist Pro designs using CSS Sculptor and CSS Menu Writer.