For my NetBSD servers, I don't rely on sysupgrade to upgrade the kernel, mainly because you may end up with incompatibles userland / kernel at some point, and as those machines are "away", I don't want to take any risk.
This is why I won't recommend the use of sysupgrade(8)'s auto
keyword for a server (I use it on my NetBSD workstations). Instead, I first upgrade the kernel, which is backward compatible, then use sysupgrade(8) to update the userland.
Also, in most cases, as I build my own NetBSD kernels for those servers in order to enable IPsec and some additional features, there's no real need for sysupgrade(8) in that area.
For most people, the following procedure will do:
$ ftp ftp://ftp.fr.netbsd.org/pub/NetBSD/NetBSD-6.1/amd64/binary/kernel/netbsd-GENERIC.gz
# cp /netbsd /onetbsd
# cp netbsd-GENERIC.gz /netbsd
# shutdown -r now
uname -r
should show the new kernel version.
# sysupgrade fetch ftp://ftp.fr.NetBSD.org/pub/NetBSD/NetBSD-6.1/$(uname -m)
# sysupgrade sets
# sysupgrade postinstall
# sysupgrade etcupdate
# sysupgrade clean
# shutdown -r now