Using google's translate, this is what I got as changelog from the Korean site:
1. Djvu file format support. (Added in firmware 1.70)
: Story Djvu files from the product supports the following features.
- Page Jump
- Bookmark
- Zoom (4 steps)
- Popup Dictionary function (if it is equipped with pre-content)
2. Adding the time set by city. (Added in firmware 1.70)
: Set → Time setting can be set in the city.
After entering the time setting off down the arrow keys to change the city can be.
I don't have any use for Djvu format, so I don't even need to upgrade. I was hoping for improvements for reading PDF files in landscape mode. Well, another 3 months wait for another update (hopefully).