For upgrading my FreeBSD box i use the binary freebsd-update. Well, i logged as root and i type:
# freebsd-update upgrade -r 9.0-RELEASE
# freebsd-update fetch
# freebsd-update install
# reboot
The system will reboot with the new kernel after the reboot, run freebsd-update install again
to install userland components and rebbot
# freebsd-update install
# reboot
You also need to update all packages, type:
# portsnap fetch update
# pkg_version -vIL=
# portupgrade -a
