Thanks a lot.
I will test later and I will let you know.
Anyway I also managed in another way: I put the SD card into another a linux machine, I opened gparted then: (the partition was recognize as 32GB as it should be but wasn't working properly)
1 Resized the partition reducing the space. Applyed this configuration 29 GB.
2 Resized the partition increasing the space up to 32 GB (more or less). In this way I bascally overwrites the sector of the previous partition "at least" in terms of table map (MFT in windows, something similar in unix).
restarting Libreelec it was able to recognize the whole space.
Regards Manu