If packages are on the local machine, they are scanned directly, otherwise the pkg_summary database is fetched.
(Using pkg_summary for local packages is on the TODO list.) (pkg_chk is also covered below.) Note: Be sure you have an updated "pkgsrc" directory.
files: this is the official description of the upgrade procedure, with platform specific information and important details.
Contents pkg_add's -u option is used to update a package.
Basically: it saves the package's current list of packages that depend on it ( REQUIRED_BY), installs the new package, and replaces that list of dependencies.
Please always refer to the output of -h and the files ) and installing the results with minimal effort.
Both of these tools have configuration files to determine how to build a release and how to install it.