Quick and dirty guide to upgrading

Update your sources in /usr/src using cvs, cvsup or whatever means you
choose.

Build them.

cd /usr/src
make buildwork
make buildkernel
make installkernel
shutdown -r now

On reboot, boot into single user mode and run:
swapon -a
fsck -p / /usr /tmp /var
mount -u /
mount /usr
mount /var
mount /tmp
cd /usr/src
mergemaster -p
make installworld
mergemaster
reboot


My variation:
cd /usr/src
sudo time nice -n 10 make buildwork buildkernel KERNCONF=CUSTOM | tee /tmp/buildworldkernel.log
sudo shutdown -r now

boot into single user:
swapon -a
fsck -p / /usr /tmp /var
mount -u /
mount /usr
mount /var
mount /tmp
cd /usr/src
mergemaster -p
time make installworld
mergemaster
reboot