sudo mv /var/www/owncloud /var/www/owncloud_bak
sudo wget https://download.nextcloud.com/server/releases/nextcloud-10.0.0.tar.bz2
sudo tar -xjf nextcloud-10.0.0.tar.bz2
sudo mv nextcloud /var/www/owncloud
sudo chown www-data: -R /var/www/owncloud
sudo find /var/www/owncloud -type d -exec chmod 755 {} \;
sudo find /var/www/owncloud -type f -exec chmod 644 {} \;
sudo cp /var/www/owncloud_bak/config/config.php /var/www/owncloud/config/
sudo chmod +x /var/www/owncloud/occ
cd /var/www/owncloud
sudo -u www-data php occ maintenance:mode --on
sudo -u www-data php occ upgrade
sudo -u www-data php occ maintenance:mode --off
https://websetnet.net/migrate-owncloud-nextcloud/