Hi Sandra
To delete books from your 505:
Through Windows Explorer on your PC -- Click on the 'Start' button and then 'Computer'. You should see your hard disk drives listed and your 505 listed as a 'removable disk'. Double click on the removable disk. I have a folder called 'database'. In the database folder is one called 'media' and within that one is a folder called 'books'. Your books should be in there and can be deleted.
On the 505 -- Select the book you want to delete. Go to the page that has 'History, Info, and Utilities' listed. Push the number 8 button next to utilities. On the Utilities page is an option to delete the book. Press the number 3 button next to Delete. To actually delete the book, you press the bookmark button.
Hope that makes sense!