Exemple: j'ai une version 12.0 et je veux passer sur une 12.1

freebsd-update -r 12.1-RELEASE upgrade

src component not installed, skipped
Looking up update.FreeBSD.org mirrors... none found.
Fetching metadata signature for 12.0-RELEASE from update.FreeBSD.org... done.
Fetching metadata index... done.
Fetching 1 metadata files... done.
Inspecting system... done.

The following components of FreeBSD seem to be installed:
kernel/generic kernel/generic-dbg world/base world/doc world/lib32

The following components of FreeBSD do not seem to be installed:
world/base-dbg world/lib32-dbg

Does this look reasonable (y/n)? y

Fetching metadata signature for 12.1-RELEASE from update.FreeBSD.org... done.
Fetching metadata index... done.
Fetching 1 metadata patches. done.
Applying metadata patches... done.
Fetching 1 metadata files... done.
Inspecting system... done.
Fetching files from 12.0-RELEASE for merging... done.
Preparing to download files... done.
Fetching 10450 patches.....10....20....30....
10450 done.
Applying patches...
The following files will be removed as part of updating to 12.1-RELEASE-p0:

freebsd-update install
src component not installed, skipped
Installing updates...
Kernel updates have been installed.  Please reboot and run
"/usr/sbin/freebsd-update install" again to finish installing updates.

reboot

uname -a
FreeBSD fbsd-1 12.1-RELEASE FreeBSD 12.1-RELEASE r354233 GENERIC  amd64

freebsd-update install
src component not installed, skipped
Installing updates...
Completing this upgrade requires removing old shared object files.
Please rebuild all installed 3rd party software (e.g., programs
installed from the ports tree) and then run "/usr/sbin/freebsd-update install"
again to finish installing updates.

reboot

freebsd-update install
src component not installed, skipped
Installing updates... done.

How To BSD