Because the official documentation is too verbose.
sudo -i
service apache2 stop
cd /var/www/owncloud
sudo -u www-data ./occ maintenance:mode --on
[make a note of the apps listed here]
sudo -u www-data ./occ app:list
cd /var/www/
sudo wget https://download.owncloud.com/server/stable/owncloud-complete-latest.tar.bz2
sudo mv /var/www/owncloud /var/www/backup_owncloud
sudo tar -xf owncloud-complete-latest.tar.bz2
sudo cp /var/www/backup_owncloud/config/*config.php /var/www/owncloud/config/
[If these files/folders don’t exist then you will get an error. It’s okay. Keep moving on.]
sudo cp /var/www/backup_owncloud/config/*.json /var/www/owncloud/config/
cd /var/www/owncloud
sudo mkdir /var/www/owncloud/apps-external
cp /var/www/backup_owncloud/apps-external/* -R /var/www/owncloud/apps-external
cp /var/www/backup_owncloud/apps/* -R /var/www/owncloud/apps
cp /var/www/backup_owncloud/.htaccess /var/www/owncloud/.htaccess
sudo find -L /var/www/owncloud \
\( -path ./data -o -path ./config \) -prune -o \
-type d -print0 | sudo xargs -0 chown root:www-data
sudo find -L /var/www/owncloud \
\( -path ./data -o -path ./config \) -prune -o \
-type f -print0 | sudo xargs -0 chown root:www-data
sudo chown -R www-data:www-data /var/www/owncloud/config
sudo chown -R www-data:www-data /var/www/owncloud/data
sudo chown -R www-data:www-data /var/www/owncloud/apps
sudo find -L /var/www/owncloud -type f -print0 | sudo xargs -0 chmod 640
sudo find -L /var/www/owncloud -type d -print0 | sudo xargs -0 chmod 750
chown www-data:www-data apps-external/ -R
sudo chmod +x /var/www/owncloud/occ
sudo -u www-data ./occ upgrade
sudo -u www-data ./occ maintenance:mode --off
service apache2 start
[check for proper login and upgraded version. If working…]
cd /var/www
rm backup_owncloud -R
rm owncloud-complete*.bz2