Internal storage is very low, help please

I have downloaded several ebooks into my library for content browsing. Now I have warning that my internal sotrage is low (total 2.13 GB, current space 884kb). Please help how can I free up the space and delete some file in library. Where is the files in library located?
Thanks

If they're in your Library, then you probably should use the Library to delete the books. Tap the new Checkmark icon at the top right of the Library screen and multiselect the books you want to delete, then tap the "Delete" button at the bottom of the Library screen.

Thank you borisb. One more question, how can I browse all the file size in internal storage so I can delete the largest file that taken up my space. Many thanks.

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.

thank you very much.

Another thing to remember is Clean the cache for any program that allows it. The browser especially. Delete old mail, move pictures music downloaded files etc to external SD card.

I use the manager on menu on ES explorer. I found that there was a lot of pdf files in .br folder with weird names . It took a huge space . How can i delete those files.

As a caution, please don't delete a file if you don't know exactly what file it is (i.e., you're the one that created the file). While deleting a PDF is probably harmless, other files may cripple your eDGe.

As for the .br folder, I'm not sure what (or where) that folder is. If it doesn't invade your privacy, can you list the names of two or three of these PDF files? It may help explain what they are.

The several pdf files that stay inside the ".br" folder (/sdcard/.br) is start with abr* and follow by number such as abr50098.pdf, taken up 81.15 MB, abr52031.pdf taken up 41.99 MB, abr15943.pdf taken 49.5 MB etc. I don't know what it represent and why it take so much space. I think it can be delete because it just pdf file.I just don't know where it is stored and how can I get rid of it and recovered my space.
Thank you Borisb. I need your help.

Those might be temporary files used by an app you installed - I don't have the directory. The name of the app may be related to the initials "BR".

If you know what app that is, then either go into that app and delete the files via the app's user interface, or go into Applications, find the app and tap it, then click the "Clear Cache" button. These options are the safest.

In any case, if you want to delete the files directly yourself, then in ES File Explorer tap and hold a file and pick "Delete" from the menu.