Probably first thing after installing an OS is to update it
apt-get update
apt-get upgrade
apt-get dist-upgrade
apt-get autoremove
This should upgrade the OS to latest debian release : Note that it only upgrades distro within its series for example 10.1 to 10.8
Checking the distro
cat /etc/os-release
Then install basic utilities.
Upgrading packages within same release
freebsd-update fetch
freebsd-update install
if anything goes wrong do this
freebsd-update rollback
For major and minor version upgrades
freebsd-update -r 13.0-RELEASE upgrade
Above command fetches generic kernel and writes config files
Installing the Upgrade
freebsd-update install
After major upgrades we need to rebuild ports
portmaster -af
freebsd-update install