It's a bit tricky but follow these instructions:
1. Launch the Journal application and start a new file (why? you'll see )
1. Launch ES File Explorer (it'll be in your Applications)
2. Press the "Menu" button, then "Manager"
3. Press "SD Card Analyst". This will take a few seconds to analyze all the file sizes in all the directories
4. When it's done, it'll show the list of folders and the % of the storage they're using
5. Tap the ".edge" folder, then the ".esi-content" folder. This is where the Library items are stored
6. All the Library items will be listed in descending file size, largest first
7. Note the largest files in the Journal
8. Press the "Home" bezel button and launch the Library
9. Use the new Search tool (magnifying glass icon) to find each one and then you can delete it.
10. If you need to, you can return to ES File Explorer by holding down the "Home" button and then tapping "ES File Explorer" in the popup

One note: when you Add to Library, you can delete the original file from your SD card, Internal Storage or wherever it was. Adding to the Library copies the file to the esi-content folder. If you don't delete the original file, you're effectively using twice the storage space for each file.