To upgrade your FreeBSD4.x server to FreeBSD4.x-STABLE, follow the instructions below:

1) If you don't have cvsup installed, install it now.
# cd /usr/ports/net/cvsup-without-gui
# make install clean

2) Enter the "/usr/share/examples/cvsup" directory.
# cd /usr/share/examples/cvsup

3) Edit the file named "stable-supfile" with your favorite text edior.
# edit stable-supfile

Change "*default host=CHANGE_THIS.FreeBSD.org" to "*default host=cvsup2.FreeBSD.org"

You can use any of FreeBSD's CVS servers.

4) Save and exit the file.

5) Execute "cvsup stable-supfile"
# cvsup stable-supfile

This will download all updates to the FreeBSD operating system

6) Enter the "/usr/src" directory.
# cd /usr/src/

7) If you need to edit your kernel, do that now
# cp sys/i386/conf/GENERIC sys/i386/conf/YOURKERNEL
# edit sys/i386/conf/YOURKERNEL

8) Build FreeBSD's world
# make buildworld

9) Build FreeBSD's kernel
# make buildkernel KERNCONF=GENERIC
-or-
# make buildkernel KERNCONF=YOURKERNEL

10) Install FreeBSD's kernel
# make installkernel KERNCONF=GENERIC
-or-
# make installkernel KERNCONF=YOURKERNEL

11) Reboot
# reboot

12) Install FreeBSD's world
# make installworld

13) Reboot
# reboot

14) Run mergemaster (This step is not required, however it should be done)
# mergemaster

15) Reboot, and you'll be running the most up to date version of FreeBSD4.x

Enjoy!

Originally posted by inFused
To upgrade your FreeBSD4.x server to FreeBSD4.x-STABLE...

You forgot step 0: Carefully consider if you actually want to do this. -STABLE is a development branch, even if it is very well tested, and it brings primarily new features. Unless you have any reason to need those features, there's no reason to run 4-STABLE; indeed, most users -- especially on production servers -- should never "make buildworld".

It's still useful for those looking to build their own kernels (as it demonstrates how to download the current kernel source code), and incase there is a security flaw discovered in the operating system.

I agree that knowing how to build a custom kernel is important; but there's no reason for anyone to recompile the world to deal with security flaws -- FreeBSD Update normally has binary updates available before the patches even reach cvsup-master, let alone any of the publicly accessible mirrors.

Originally posted by cperciva
I agree that knowing how to build a custom kernel is important; but there's no reason for anyone to recompile the world to deal with security flaws
Unless a bug in OpenSSL like this one is discovered :
ftp://ftp.freebsd.org/pub/FreeBSD/CERT/advisories/FreeBSD-SA-04:05.openssl.asc
and the best solution recommended by FreeBSD team is to rebuild the world.