Hi
I have created an Ubuntu LiveUSB stick using Rufus and a downloaded ISO file (ubuntu-18.04.1-desktop-amd64.iso) from the Ubuntu website.
I then booted up in to Ubuntu off the USB stick and installed gparted. Ctrl + Alt + T to open terminal then this command:
I then shrank my Storage partition a little bit and then increased the system partition from 242MB to 512MB.
I then updated the LibreElec install successfully to version 9.0.0 by manually extracting the .img file (LibreELEC-Generic.x86_64-9.0.0.img) from the .img.gz file and placing it in the Update folder and then rebooted the PC.
It now says Kodi v18 Leia - Database migration in progress please wait.
I now see there is a bootable version of gparted as you said, so probably could have done it that way and not bothered with the Ubuntu LiveUSB OS.
Before I did any of this I took a full disk backup image using Acronis True Image and I also did a backup in the LibreElec configuration add-on in Kodi just to be on the safe side and copied the .tar file off the system.