1. Add the LibreOffice 6.0 PPA
The LibreOffice Fresh PPA is maintained by LibreOffice. It provides latest packages of the open source office suite for use on Ubuntu 16.04 LTS, Ubuntu 17.10 and Ubuntu 18.04 (though the latter shouldn’t need to as LibreOffice 6.0 is included by default).
This PPA will work on Ubuntu, Linux Mint and most other Ubuntu-based distros.
To add the LibreOffice Fresh PPA open a new Terminal window and run this command:
sudo add-apt-repository ppa:libreoffice/ppa
2. Update Your System
Next run this command to update the list of packages available to install on your system:
sudo apt update
3. Upgrade or Install LibreOffice 6.0
Finally, run this command to upgrade or install LibreOffice 6.0:
sudo apt install libreoffice
Once this command completes you can head to your application launcher of choice and launch LibreOffice.
To verity your upgrade went successfully just head to the Help > About option. You should see the correct version listed.
原文：https://www.omgubuntu.co.uk/2018/02/install-libreoffice-6-0-on-ubuntu