This article only shows how to do upgrades across releases. It is fairly straight forward, though like any OS, doing a major upgrade of this type requires patience, especially as with FreeBSD the entire ports and binary libraries are upgraded also.

For now, a simple block of code followed by some references

upgrade.sh

# NOTE: this is NOT a bash script. For one thing, sh is used for BSD
# and for another, there are several places where you have to provide input
 
# get latest release info
freebsd-update fetch
freebsd-update install
# download upgrade files. Change the 10.3-RELEASE to
# whatever release you are upgrading to.
freebsd-update upgrade -r 10.3-RELEASE
# do the initial upgrade
freebsd-update install
# reboot
shutdown -r now
# update everything else
freebsd-update install
shutdown -r now
 
# upgrade ports structure
portsnap fetch
portsnap extract
portsnap fetch update
 
# upgrade pkg (binary) packages
pkg clean
pkg update
pkg upgrade

• https://www.freebsd.org/releases/ is a list of current releases
• https://www.freebsd.org/releases/10.3R/installation.html are the notes for 10.3
• https://www.freebsd.org/ports/index.html