Upgrade OpenBSD

Read the official FAQ first. Backup all your data first, then verify your backups. Download the install image and verify its checksum:

# PKG_PATH='http://fastly.cdn.openbsd.org/pub/OpenBSD'
# ftp $PKG_PATH/6.3/amd64/install63.fs
# ftp $PKG_PATH/6.3/amd64/SHA64.sig
# sha256 -C SHA256.sig install63.fs
(SHA256) install63.fs: OK

Plug in and check your USB flash drive:

# dmesg | grep removable | tail -n1
sd3 at scsibus5 targ 1 lun 0: <Vendor, Model, 1.11>
SCSI3 0/direct removable serial.12345678901234567890987654

In my case it appears as sd3. Now you can copy the installer image to the USB flash drive. Be extremely cautious:

# dd if=install63.fs of=/dev/rsd3c bs=1m

Boot from that USB drive, then choose the (S)hell option to mount your encrypted disk.

# bioctl -c C -l /dev/sd0c softraid0
scsibus1 at softraid0: 1 targets
sd2 at scsibus2 targ 0 lun 0: <OPENBSD, SR RAID 1, 005>
SCSI2 0/direct fixed
sd2: 10244MB, 512 bytes/sec, 20980362 sec total
# exit

Choose the (U)pgrade option and follow the prompts.