You normally don’t need to delete/uninstall LibreOffice (or any program for that matter) on the Mac. Download LibreOffice from https://www.libreoffice.org, open the .dmg file and drag the LibreOffice icon to the Applications folder. If LibreOffice is already installed, you’ll be asked if you want to either replace, keep both or cancel. If you select “Replace” you are effectively updating the existing installation.
If you decide you want to uninstall the existing LibreOffice by dragging the app to the Trash be aware that you’ll leave behind various existing settings and preferences.