Installing updates manually via FTP
This process is very, very similar to installing via FTP. The only real difference is that the easy-digital-downloads folder will already exist.
First go to the WordPress plugins repository at https://wordpress.org/plugins/ and search for Easy Digital Downloads. Then click on the Easy Digital Downloads link.
Then when you're on the Easy Digital Downloads page, click on the download link.
Once you have the zip file, open it (typically by double clicking it) and inside you'll file a folder called easy-digital-downloads.
This is where things differ from the install. Now you want to take the CONTENTS of the easy-digital-downloads folder, and put them inside the easy-digital-downloads folder that exists on the server.
Now go to the Plugins page in your WordPress admin area, find Easy Digital Downloads and deactivate and immediately reactivate it. This allows its install hooks to fire and check for database updates etc.
Then you're finished.