Problem during Update

I cannot update my owncloud instance.
When I log on, I am greeted with

I go to the Admin page and click on "Open Updater" where I get:

Current version is "ownCloud 9.0.8 (stable)"

Hi,

please don't rely on the updater app (this is known to have various different issues) and just do a manual update as explained here:

https://doc.owncloud.org/server/latest/admin_manual/maintenance/manual_upgrade.html

I followed the steps up to where I had to run the update script, which told me I had to install a more recent version of php, which I duly did as described under

Running "php -v" now gives me:

2 {main}root@raspberry:/mnt/usb/owncloud# php -v

PHP 5.6.13 (cli) (built: May 4 2017 22:52:47)
Copyright (c) 1997-2015 The PHP Group
Zend Engine v2.6.0, Copyright (c) 1998-2015 Zend Technologies

However, when I try to run the update script, I get:

root@raspberry:/mnt/usb/owncloud# sudo -u www-data php occ upgrade
The process control (PCNTL) extensions are required in case you want to interrupt long running commands - see http://php.net/manual/en/book.pcntl.php
ownCloud or one of the apps require upgrade - only a limited number of commands are available
You may use your browser or the occ upgrade command to do the upgrade
PHP module zip not installed.
Please ask your server administrator to install the module.

PHP module mb multibyte not installed.
Please ask your server administrator to install the module.

PHP module GD not installed.
Please ask your server administrator to install the module.

PHP module zlib not installed.
Please ask your server administrator to install the module.

PHP module cURL not installed.
Please ask your server administrator to install the module.

An unhandled exception has been thrown:
exception 'Exception' with message 'Environment not properly prepared.' in /mnt/usb/owncloud/lib/private/Console/Application.php:134
Stack trace:

0 /mnt/usb/owncloud/console.php(98): OC\Console\Application->loadCommands(Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))

1 /mnt/usb/owncloud/occ(11): require_once('/mnt/usb/ownclo...')