Use the Sony eReader store program, don't go directly to the ereader site. Once in there click in the left hand pane the "eBook Store". In the right hand pane you should be brought to the main site of the reader store. Look at the top towards the left hand side you will see a sign in link, click it and sign into your Reader store account. Once you're logged in click on the "My Account" link that will be in the same spot. Once you're in your "My Account" Page, look towards the middle where it is titled "My Library", click on the "View / Download purchased eBooks" link. If you have alot of books to download again, scroll to the bottom and check off the "Check all on this page" then click on the "Download all checked" button.
You have to do this through the sony program. If you don't have the latest edition installed, go here :
http://ebookstore.sony.com/download/
The Adobe Digital Edition will not convert files to epub, it only allows you to authorize up to 6 devices to use the epub file on.