Boot GParted Live from a thumb drive on your Windows PC, and follow plan A.
Thank you all for the support.
I followed Da Flex advice and it was a success. It took a while though.
I share my experience here for those who are interested.
First, i have to say that i use libreelec on an intel nuc7. I downloaded Gparted from the official website and created a booatble usb using balena etcher with the downloaded ISO.
The last release was not good for me. I had a black screen after the boot. I had issues with display setup. The solution was to use the 0.33 release witch worked fine with the default settings.
When gparted booted correctly, the steps were:
1. Shrink the ntfs partition to the minimum allowed regarding the sise of my library. The process took 12 hours.
2. Create a ext4 partition on the freed disc space.
3. Boot on libreelec
4. Copy all the data from ntfs partition to ext4 partition using the librelec file manager. The process took 10 hours.
5. Rebooted with gparted.
6. Ereased ntfs partition.
7. Extended the ext4 partition to fit the entire hdd size. The process took 12 hours
8. Renamed the ext4 partition to match the old ntfs partition.
9. Rebooted librelec... the library is here...no thing to do.
After a week of testing, i have no corruption of hdd and random not mounting hdd as i had with the ntfs partition.