safe-upgrade
           Upgrades installed packages to their most recent version. Installed
           packages will not be removed unless they are unused (see the
           section “Managing Automatically Installed Packages” in the aptitude
           reference manual); packages which are not currently installed will
           not be installed.

           It is sometimes necessary to remove or install one package in order
           to upgrade another; this command is not able to upgrade packages in
           such situations. Use the full-upgrade command to upgrade as many
           packages as possible.

       full-upgrade
           Upgrades installed packages to their most recent version, removing
           or installing packages as necessary. This command is less
           conservative than safe-upgrade and thus more likely to perform
           unwanted actions. However, it is capable of upgrading packages that
           safe-upgrade cannot upgrade.

           Note
           This command was originally named dist-upgrade for historical
           reasons, and aptitude still recognizes dist-upgrade as a synonym
           for full-upgrade.