I have a couple KVM machines:

    1   l ~/VMs
    2   -rw-r--r--   1 void users 1,986,002,944 09-17 09:11 | archlinux-current.qcow2
    3   -rw-r--r--   1 void users 2,451,505,152 09-17 09:14 | centos-7.qcow2
    4   -rw-r--r--   1 void users 3,032,350,720 09-17 10:06 | freebsd-103.qcow2
    5   -rw-r--r--   1 void users 1,813,512,192 05-20 20:03 | netbsd-70.qcow2
    6   -rw-r--r--   1 void users   843,251,712 05-20 18:55 | openbsd-59.qcow2
    7   -rw-r--r--   1 void users 6,452,215,808 09-17 09:21 | ubuntu-1204.qcow2
    8   -rw-r--r--   1 void users 6,224,478,208 09-17 09:22 | ubuntu-1404.qcow2
    9   -rw-r--r--   1 void users 4,264,034,304 09-17 09:24 | ubuntu-1604.qcow2

  Only for testing purposes. "Does $foo run on $bar?"

  I  upgraded  my  FreeBSD  box  from 10.2 to 10.3 today. I followed the
  guide at [1].  It took pretty long, almost 1.5  hours,  but  this  may
  have been due to slow internet.

  Upgrading  OpenBSD from 5.9 to 6.0 was much quicker. I booted into the
  install kernel, hit a few buttons, and was done.

  NetBSD (7.0 to 7.0.1) was pretty easy, too. Boot from an  installation
  ISO, choose "upgrade" and wait. Didn't take long.

  This  was  the first time that I actually upgraded these BSD boxes. In
  the past, I simply did a clean reinstall from scratch. I also used  to
  think  that  BSD upgrades are painful. In the past, this may have been
  true -- no idea, really, I never went through. But these few  upgrades
  today were just a piece of cake.

  Of  course,  since  those  are  only  base  images,  I  don't have any
  additional packages/ports installed. Just the base systems. This makes
  things easier.

  ____________________

  1. https://www.freebsd.org/releases/10.3R/installation.html#upgrade-binary