To change the format of your book from A4 lay flat to A4 standard using the Picasso Album Maker program for Windows, you will need to access the program's settings or preferences. Look for options related to book format or page layout. If there is an option to switch between A4 lay flat and A4 standard, you can select the desired format and save the changes. If such an option is not available within the program, you might need to contact the software's support team for assistance.