Hi Peter,

you cand find a description of these commands with man:

$ man apt-get

update
    update is used to resynchronize the package index files from their
    sources. The indexes of available packages are fetched from the
    location(s) specified in /etc/apt/sources.list. For example, when
    using a Debian archive, this command retrieves and scans the
    Packages.gz files, so that information about new and updated
    packages is available. An update should always be performed before
    an upgrade or dist-upgrade. Please be aware that the overall
    progress meter will be incorrect as the size of the package files
    cannot be known in advance.

upgrade
    upgrade is used to install the newest versions of all packages
    currently installed on the system from the sources enumerated in
    /etc/apt/sources.list. Packages currently installed with new
    versions available are retrieved and upgraded; under no
    circumstances are currently installed packages removed, or packages
    not already installed retrieved and installed. New versions of
    currently installed packages that cannot be upgraded without
    changing the install status of another package will be left at
    their current version. An update must be performed first so that
    apt-get knows that new versions of packages are available.

In other words, update is just a “what is new?” question and upgrade is the installation itself. So what you need is:

(sudo) apt-get update && (sudo) apt-get upgrade