On a wide webpage you should see pianobook and logo on the left with LIBRARY, CONTRIBUTE, ABOUT, STORIES and FORUM.
Click on LIBRARY and select a category and find a library.
On a narrow webpage you will instead see MENU on the right, and that will take you to LIBRARY, CONTRIBUTE, ABOUT, STORIES and FORUM.
Find the library/instrument and scroll down to the DOWNLOADS. Beneath that will be the formats that it is available in – highlighted in blue font, and if there is one for the sampler that you are using click on that and it will bring the downloadable zip file to the bottom of your webpage. Click on Save as…