$ freebsd-update -r 11.2-RELEASE upgrade
Looking up update.FreeBSD.org mirrors... 2 mirrors found.
Fetching metadata signature for 11.1-RELEASE from update4.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 src/src world/base world/lib32

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

Does this look reasonable (y/n)? y

Fetching metadata signature for 11.2-RELEASE from update4.freebsd.org... done.
Fetching metadata index... done.
Fetching 1 metadata patches. done.
Applying metadata patches... done.
Fetching 1 metadata files... 
Inspecting system... 
done.
Fetching files from 11.1-RELEASE for merging... done.
Preparing to download files...
...

$ shutdown -r now
(system reboots)

$ freebsd-update install
Installing updates...
 done.
$ freebsd-version -u         
11.2-RELEASE-p3
$ freebsd-version -k
11.2-RELEASE-p3
$ freebsd-version -r
11.2-RELEASE-p3