There are three methods for updating a FreeBSD system: from source, binary updates, and the installation discs.
Updating from source is the most involved update method, but offers the greatest amount of flexibility. The process involves synchronizing a local copy of the FreeBSD source code with the FreeBSD Subversion servers. Once the local source code is up to date you can build new versions of the kernel and userland. For more information on source updates see the chapter on updating in the FreeBSD Handbook.
Binary updates are similar to using yum or apt-get to update a Linux® system. The command freebsd-update(8) will fetch new updates and install them. The updates can be scheduled using cron(8).
Note: If you do use cron(8) to schedule the updates, please be sure to use freebsd-update cron in your crontab(1) to reduce the possibility of a large number of machines all pulling updates at the same time.
0 3 * * * root /usr/sbin/freebsd-update cron
The last update method, updating from the installation discs, is a straight-forward process. Boot from the installation discs and select the option to upgrade.