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.