Tested on OpenBSD 6.4

Upgrade OpenBSD on OpenBSD.Amsterdam

If you have OpenBSD 6.3 installed on your VM and want to upgrate it, then backup your data first.

Prepare

Login to your VM, download, and verify bsd.rd:

# ftp -V https://cdn.openbsd.org/pub/OpenBSD/6.4/amd64/bsd.rd
bsd.rd       100% |*******************************|  9782 KB    00:00
# ftp -V https://cdn.openbsd.org/pub/OpenBSD/6.4/amd64/SHA256.sig
SHA256.sig   100% |*******************************|  2141       00:00
# signify -C -p /etc/signify/openbsd-64-base.pub -x SHA256.sig bsd.rd
Signature Verified
bsd.rd: OK
# cp /bsd.rd /bsd.rd.63
# cp bsd.rd /
#

Read the official FAQ.

Update your configuration files, if needed for 6.4.

Access the console

Login to your OpenBSD.Amsterdam server (find the HOSTNAME, PORT, and ID in the email message you got after the registration):

$ ssh \
-p PORT \
-e none \
-o VerifyHostKeyDNS=ask \
HOSTNAME.openbsd.amsterdam \
vmctl console ID

Hit Enter to see the console.

Upgrade

Login via the console and boot from /bsd.rd.

OpenBSD/amd64 (xxx.xxx.xx) (tty00)

login: root
password: ********

OpenBSD 6.3 (GENERIC) #100: Sat Mar 24 14:17:45 MDT 2018
...
# reboot
...
>> OpenBSD/amd64 BOOT 3.41
boot> boot /bsd.rd

booting hd0a:/bsd.rd: 3511114+1500160+3892040+0+598016
...

Choose (A)utoinstall:

Welcome to the OpenBSD/amd64 6.4 installation program.
(I)nstall, (U)pgrade, (A)utoinstall or (S)hell? a
...
CONGRATULATIONS! Your OpenBSD upgrade has been successfully completed!
...
>> OpenBSD/amd64 BOOT 3.41
boot> boot /bsd
...

OpenBSD/amd64 (s1.romanzolotarev.com) (tty00)

login:

Type ~. to close the console.

Update packages

Login and update the installed packages:

# pkg_add -uv
...
#