Cvsup source

Then

# cd /usr/src

# make buildworld

# make buildkernel KERNCONF=MYKERNEL

# make installkernel KERNCONF=MYKERNEL

# shutdown now

# fsck -p

# mount -u /

# mount -a -t ufs

# swapon -a

# mergemaster -p

# make installworld

# mergemaster

# reboot